Starting with version 2.4.0 SDCC in 2004 uses a time-based release schedule with one official release usually during the first half of the year.
The last digit of an official release is zero. Additionally there are daily snapshots available at http://sdcc.sourceforge.net/snap.php, and you can always build the very last version from the source code available at Sourceforge http://sdcc.sourceforge.net/snap.php#Source. The SDCC Wiki at http://sdcc.sourceforge.net/wiki/also holds some information about past and future releases.