diff --git src/wp-includes/class-wp-customize-manager.php src/wp-includes/class-wp-customize-manager.php
index 1f5da60..e4e7d9f 100644
--- src/wp-includes/class-wp-customize-manager.php
+++ src/wp-includes/class-wp-customize-manager.php
@@ -971,6 +971,32 @@ final class WP_Customize_Manager {
 			$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, $changeset_data['nav_menus_created_posts']['value'] );
 		}
 
+		// Make an index of all the posts needed and what their slugs are.
+		$needed_posts = array();
+		$attachments = $this->prepare_starter_content_attachments( $attachments );
+		foreach ( $attachments as $attachment ) {
+			$key = 'attachment:' . $attachment['post_name'];
+			$needed_posts[ $key ] = true;
+		}
+		foreach ( array_keys( $posts ) as $post_symbol ) {
+			if ( empty( $posts[ $post_symbol ]['post_name'] ) && empty( $posts[ $post_symbol ]['post_title'] ) ) {
+				unset( $posts[ $post_symbol ] );
+				continue;
+			}
+			if ( empty( $posts[ $post_symbol ]['post_name'] ) ) {
+				$posts[ $post_symbol ]['post_name'] = sanitize_title( $posts[ $post_symbol ]['post_title'] );
+			}
+			if ( empty( $posts[ $post_symbol ]['post_type'] ) ) {
+				$posts[ $post_symbol ]['post_type'] = 'post';
+			}
+			$needed_posts[ $posts[ $post_symbol ]['post_type'] . ':' . $posts[ $post_symbol ]['post_name'] ] = true;
+		}
+		$all_post_slugs = array_merge(
+			wp_list_pluck( $attachments, 'post_name' ),
+			wp_list_pluck( $posts, 'post_name' )
+		);
+
+		// Re-use auto-draft starter content posts referenced in the current customized state.
 		$existing_starter_content_posts = array();
 		if ( ! empty( $starter_content_auto_draft_post_ids ) ) {
 			$existing_posts_query = new WP_Query( array(
@@ -984,50 +1010,32 @@ final class WP_Customize_Manager {
 			}
 		}
 
+		// Re-use non-auto-draft posts.
+		if ( ! empty( $all_post_slugs ) ) {
+			$existing_posts_query = new WP_Query( array(
+				'post_name__in' => $all_post_slugs,
+				'post_status' => array_diff( get_post_stati(), array( 'auto-draft' ) ),
+				'post_type' => 'any',
+				'number' => -1,
+			) );
+			foreach ( $existing_posts_query->posts as $existing_post ) {
+				$key = $existing_post->post_type . ':' . $existing_post->post_name;
+				if ( isset( $needed_posts[ $key ] ) && ! isset( $existing_starter_content_posts[ $key ] ) ) {
+					$existing_starter_content_posts[ $key ] = $existing_post;
+				}
+			}
+		}
+
 		// Attachments are technically posts but handled differently.
 		if ( ! empty( $attachments ) ) {
-			// Such is The WordPress Way.
-			require_once( ABSPATH . 'wp-admin/includes/file.php' );
-			require_once( ABSPATH . 'wp-admin/includes/media.php' );
-			require_once( ABSPATH . 'wp-admin/includes/image.php' );
 
 			$attachment_ids = array();
 
 			foreach ( $attachments as $symbol => $attachment ) {
-
-				// A file is required and URLs to files are not currently allowed.
-				if ( empty( $attachment['file'] ) || preg_match( '#^https?://$#', $attachment['file'] ) ) {
-					continue;
-				}
-
-				$file_array = array();
-				$file_path = null;
-				if ( file_exists( $attachment['file'] ) ) {
-					$file_path = $attachment['file']; // Could be absolute path to file in plugin.
-				} elseif ( is_child_theme() && file_exists( get_stylesheet_directory() . '/' . $attachment['file'] ) ) {
-					$file_path = get_stylesheet_directory() . '/' . $attachment['file'];
-				} elseif ( file_exists( get_template_directory() . '/' . $attachment['file'] ) ) {
-					$file_path = get_template_directory() . '/' . $attachment['file'];
-				} else {
-					continue;
-				}
-				$file_array['name'] = basename( $attachment['file'] );
-
-				// Skip file types that are not recognized.
-				$checked_filetype = wp_check_filetype( $file_array['name'] );
-				if ( empty( $checked_filetype['type'] ) ) {
-					continue;
-				}
-
-				// Ensure post_name is set since not automatically derived from post_title for new auto-draft posts.
-				if ( empty( $attachment['post_name'] ) ) {
-					if ( ! empty( $attachment['post_title'] ) ) {
-						$attachment['post_name'] = sanitize_title( $attachment['post_title'] );
-					} else {
-						$attachment['post_name'] = sanitize_title( preg_replace( '/\.\w+$/', '', $file_array['name'] ) );
-					}
-				}
-
+				$file_array = array(
+					'name' => $attachment['file_name'],
+				);
+				$file_path = $attachment['file_path'];
 				$attachment_id = null;
 				$attached_file = null;
 				if ( isset( $existing_starter_content_posts[ 'attachment:' . $attachment['post_name'] ] ) ) {
@@ -1080,14 +1088,14 @@ final class WP_Customize_Manager {
 				}
 
 				$attachment_ids[ $symbol ] = $attachment_id;
-				$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, array_values( $attachment_ids ) );
 			}
+			$starter_content_auto_draft_post_ids = array_merge( $starter_content_auto_draft_post_ids, array_values( $attachment_ids ) );
 		}
 
 		// Posts & pages.
 		if ( ! empty( $posts ) ) {
 			foreach ( array_keys( $posts ) as $post_symbol ) {
-				if ( empty( $posts[ $post_symbol ]['post_type'] ) ) {
+				if ( empty( $posts[ $post_symbol ]['post_type'] ) || empty( $posts[ $post_symbol ]['post_name'] ) ) {
 					continue;
 				}
 				$post_type = $posts[ $post_symbol ]['post_type'];
@@ -1241,6 +1249,69 @@ final class WP_Customize_Manager {
 	}
 
 	/**
+	 * Prepare starter content attachments.
+	 *
+	 * Ensure that the attachments are valid and that they have slugs and file name/path.
+	 *
+	 * @since 4.7.0
+	 * @access private
+	 *
+	 * @param array $attachments Attachments.
+	 * @return array Prepared attachments.
+	 */
+	protected function prepare_starter_content_attachments( $attachments ) {
+		$prepared_attachments = array();
+		if ( empty( $attachments ) ) {
+			return $prepared_attachments;
+		}
+
+		// Such is The WordPress Way.
+		require_once( ABSPATH . 'wp-admin/includes/file.php' );
+		require_once( ABSPATH . 'wp-admin/includes/media.php' );
+		require_once( ABSPATH . 'wp-admin/includes/image.php' );
+
+		foreach ( $attachments as $symbol => $attachment ) {
+
+			// A file is required and URLs to files are not currently allowed.
+			if ( empty( $attachment['file'] ) || preg_match( '#^https?://$#', $attachment['file'] ) ) {
+				continue;
+			}
+
+			$file_path = null;
+			if ( file_exists( $attachment['file'] ) ) {
+				$file_path = $attachment['file']; // Could be absolute path to file in plugin.
+			} elseif ( is_child_theme() && file_exists( get_stylesheet_directory() . '/' . $attachment['file'] ) ) {
+				$file_path = get_stylesheet_directory() . '/' . $attachment['file'];
+			} elseif ( file_exists( get_template_directory() . '/' . $attachment['file'] ) ) {
+				$file_path = get_template_directory() . '/' . $attachment['file'];
+			} else {
+				continue;
+			}
+			$file_name = basename( $attachment['file'] );
+
+			// Skip file types that are not recognized.
+			$checked_filetype = wp_check_filetype( $file_name );
+			if ( empty( $checked_filetype['type'] ) ) {
+				continue;
+			}
+
+			// Ensure post_name is set since not automatically derived from post_title for new auto-draft posts.
+			if ( empty( $attachment['post_name'] ) ) {
+				if ( ! empty( $attachment['post_title'] ) ) {
+					$attachment['post_name'] = sanitize_title( $attachment['post_title'] );
+				} else {
+					$attachment['post_name'] = sanitize_title( preg_replace( '/\.\w+$/', '', $file_name ) );
+				}
+			}
+
+			$attachment['file_name'] = $file_name;
+			$attachment['file_path'] = $file_path;
+			$prepared_attachments[ $symbol ] = $attachment;
+		}
+		return $prepared_attachments;
+	}
+
+	/**
 	 * Save starter content changeset.
 	 *
 	 * @since 4.7.0
diff --git src/wp-includes/post.php src/wp-includes/post.php
index 620d1e4..2c70fdd 100644
--- src/wp-includes/post.php
+++ src/wp-includes/post.php
@@ -3673,7 +3673,7 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 
 	if ( 'attachment' == $post_type ) {
 		// Attachment slugs must be unique across all types.
-		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND ID != %d LIMIT 1";
+		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_status != 'auto-draft' AND post_name = %s AND ID != %d LIMIT 1";
 		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_ID ) );
 
 		/**
@@ -3701,7 +3701,7 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 		 * Page slugs must be unique within their own trees. Pages are in a separate
 		 * namespace than posts so page slugs are allowed to overlap post slugs.
 		 */
-		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND post_type IN ( %s, 'attachment' ) AND ID != %d AND post_parent = %d LIMIT 1";
+		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_status != 'auto-draft' AND post_name = %s AND post_type IN ( %s, 'attachment' ) AND ID != %d AND post_parent = %d LIMIT 1";
 		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_type, $post_ID, $post_parent ) );
 
 		/**
@@ -3725,7 +3725,7 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 		}
 	} else {
 		// Post slugs must be unique across all posts.
-		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND post_type = %s AND ID != %d LIMIT 1";
+		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_status != 'auto-draft' AND post_name = %s AND post_type = %s AND ID != %d LIMIT 1";
 		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_type, $post_ID ) );
 
 		// Prevent new post slugs that could result in URLs that conflict with date archives.
diff --git tests/phpunit/tests/post/wpUniquePostSlug.php tests/phpunit/tests/post/wpUniquePostSlug.php
index 536017d..a728454 100644
--- tests/phpunit/tests/post/wpUniquePostSlug.php
+++ tests/phpunit/tests/post/wpUniquePostSlug.php
@@ -347,4 +347,46 @@ class Tests_Post_WpUniquePostSlug extends WP_UnitTestCase {
 		$found = wp_unique_post_slug( 'embed', $p, 'publish', 'attachment', 0 );
 		$this->assertSame( 'embed-2', $found );
 	}
+
+	/**
+	 * @ticket 38928
+	 */
+	public function test_non_unique_slugs_for_existing_auto_draft_posts() {
+		$auto_draft_post_id = self::factory()->post->create( array(
+			'post_type' => 'post',
+			'post_name' => 'existing-post',
+			'post_status' => 'auto-draft',
+		) );
+		$auto_draft_page_id = self::factory()->post->create( array(
+			'post_type' => 'page',
+			'post_name' => 'existing-page',
+			'post_status' => 'auto-draft',
+		) );
+		$auto_draft_attachment_id = self::factory()->attachment->create_object( 'image.jpg', $auto_draft_page_id, array(
+			'post_mime_type' => 'image/jpeg',
+			'post_type' => 'attachment',
+			'post_name' => 'existing-attachment',
+			'post_status' => 'auto-draft',
+		) );
+
+		$post_id = self::factory()->post->create( array( 'post_type' => 'post' ) );
+		$page_id = self::factory()->post->create( array( 'post_type' => 'page' ) );
+		$attachment_id = self::factory()->attachment->create_object( 'image2.jpg', $page_id, array(
+			'post_mime_type' => 'image/jpeg',
+			'post_type' => 'attachment',
+			'post_name' => 'existing-image',
+		) );
+
+		$this->assertEquals( 'existing-post', wp_unique_post_slug( 'existing-post', $post_id, 'publish', get_post_type( $post_id ), 0 ) );
+		wp_publish_post( $auto_draft_post_id );
+		$this->assertEquals( 'existing-post-2', wp_unique_post_slug( 'existing-post', $post_id, 'publish', get_post_type( $post_id ), 0 ) );
+
+		$this->assertEquals( 'existing-page', wp_unique_post_slug( 'existing-page', $page_id, 'publish', get_post_type( $page_id ), 0 ) );
+		wp_publish_post( $auto_draft_page_id );
+		$this->assertEquals( 'existing-page-2', wp_unique_post_slug( 'existing-page', $page_id, 'publish', get_post_type( $page_id ), 0 ) );
+
+		$this->assertEquals( 'existing-attachment', wp_unique_post_slug( 'existing-attachment', $attachment_id, 'publish', get_post_type( $attachment_id ), 0 ) );
+		wp_publish_post( $auto_draft_attachment_id );
+		$this->assertEquals( 'existing-attachment-2', wp_unique_post_slug( 'existing-attachment', $attachment_id, 'publish', get_post_type( $attachment_id ), 0 ) );
+	}
 }