Index: src/wp-includes/formatting.php
===================================================================
--- src/wp-includes/formatting.php	(revision 28758)
+++ src/wp-includes/formatting.php	(working copy)
@@ -100,6 +100,16 @@
 		// Pattern-based replacements of characters.
 		$dynamic = array();
 
+		// '99' is an ambiguous case among other patterns; assume it's an abbreviated year at the end of a quotation.
+		if ( "'" !== $apos && "'" !== $closing_single_quote ) {
+			$dynamic[ '/\'(\d\d)\'(?=\Z|[.,)}>\-\]]|' . $spaces . ')/' ] = $apos . '$1' . $closing_single_quote;
+		}
+
+		// '99 '99s '99's (apostrophe)  But never '9 or '999 or '99.0.
+		if ( "'" !== $apos ) {
+			$dynamic[ '/\'(?=\d\d(?:\Z|(?!\d|[.,]\d)))/' ] = $apos;
+		}
+
 		// Quoted Numbers like "42" or '42.00'
 		if ( '"' !== $opening_quote && '"' !== $closing_quote ) {
 			$dynamic[ '/(?<=\A|' . $spaces . ')"(\d[\d\.\,]*)"/' ] = $opening_quote . '$1' . $closing_quote;
@@ -108,11 +118,6 @@
 			$dynamic[ '/(?<=\A|' . $spaces . ')\'(\d[\d\.\,]*)\'/' ] = $opening_single_quote . '$1' . $closing_single_quote;
 		}
 
-		// '99 '99s '99's (apostrophe)
-		if ( "'" !== $apos ) {
-			$dynamic[ '/\'(?=\d)/' ] = $apos;
-		}
-
 		// Single quote at start, or preceded by (, {, <, [, ", -, or spaces.
 		if ( "'" !== $opening_single_quote ) {
 			$dynamic[ '/(?<=\A|[([{<"\-]|' . $spaces . ')\'/' ] = $opening_single_quote;
Index: tests/phpunit/tests/formatting/WPTexturize.php
===================================================================
--- tests/phpunit/tests/formatting/WPTexturize.php	(revision 28758)
+++ tests/phpunit/tests/formatting/WPTexturize.php	(working copy)
@@ -1279,4 +1279,87 @@
 			),
 		);
 	}
-}
+
+	/**
+	 * Year abbreviations consist of exactly two digits.
+	 *
+	 * @ticket 26850
+	 * @dataProvider data_quotes_and_dashes
+	 */
+	function test_year_abbr( $input, $output ) {
+		return $this->assertEquals( $output, wptexturize( $input ) );
+	}
+
+	function data_year_abbr() {
+		return array(
+			array(
+				"word '99 word",
+				"word &#8217;99 word",
+			),
+			array(
+				"word '99. word",
+				"word &#8217;99. word",
+			),
+			array(
+				"word '99, word",
+				"word &#8217;99, word",
+			),
+			array(
+				"word '99; word",
+				"word &#8217;99; word",
+			),
+			array(
+				"word '99' word", // For this pattern, prime doesn't make sense.  Should get apos and a closing quote.
+				"word &#8217;99&#8217; word",
+			),
+			array(
+				"word '99'. word",
+				"word &#8217;99&#8217;. word",
+			),
+			array(
+				"word '99', word",
+				"word &#8217;99&#8217;, word",
+			),
+			array(
+				"word '99.' word",
+				"word &#8217;99.&#8217; word",
+			),
+			array(
+				"word '99",
+				"word &#8217;99",
+			),
+			array(
+				"'99 word",
+				"&#8217;99 word",
+			),
+			array(
+				"word '999 word", // Does not match the apos pattern, should be opening quote.
+				"word &#8216;999 word",
+			),
+			array(
+				"word '9 word",
+				"word &#8216;9 word",
+			),
+			array(
+				"word '99.9 word",
+				"word &#8216;99.9 word",
+			),
+			array(
+				"word '999",
+				"word &#8216;999",
+			),
+			array(
+				"word '9",
+				"word &#8216;9",
+			),
+			array(
+				"in '4 years, 3 months,' Obama cut the deficit",
+				"in &#8216;4 years, 3 months,&#8217; Obama cut the deficit",
+			),
+			array(
+				"testing's '4' through 'quotes'",
+				"testing&#8217;s &#8216;4&#8217; through &#8216;quotes&#8217;",
+			),
+		);
+	}
+}
\ No newline at end of file