Historically there often were long delays between official releases and the sourceforge download area tended to get not updated at all. Starting with version 2.4.0 SDCC in 2004 switched to a time-based release schedule with one official release usually during the first half of the year.
The medium digit in the version number denotes the year of the release and the last digit of an official release is zero. Additionally there are daily snapshots available at snap http://sdcc.sourceforge.net/snap.php, and you can always build the very last version from the source code available at Source http://sdcc.sourceforge.net/snap.php#Source. The SDCC Wiki at http://sdcc.wiki.sourceforge.net/also holds some information about past and future releases.