In some rows of sortable tables stay not the full qualified date, but only the year is known. The enhanchment is, that this is detected by tablesorter. Example:
{| class="wikitable sortable"
! data-sort-type="date" |"Date"
|-
| 1. 1. 2000
|-
| 2011
|-
| about 1900
|-
| 2010<ref>cite</ref>
|}Today (2013-01-25) only the first row is a 'date'. To prevent mistake in auto detecting parser this should work only if data-sort-type="date" is spezified.
Sugestion: add folow code at row 926 in jquery.tablesorter.js:
} else if ( ( match = s.match( new RegExp( /(\d{2,4})/) ) ) !== null ) { // only year
s = [ match[1], '99', '99' ];