OK, it wasn’t just me. Apple has changed the naming scheme for Mac OS X security updates:
The naming scheme of Apple Security Updates has changed from a date
format (e.g., “Security Update 2004-12-02”) to a format based on the
year and a sequence number: Security Update YYYY-NNN. For example,
the update released today is named “Security Update 2005-001”, the
next would be “Security Update 2005-002” and so on.