In ASE 12, the dbids of the following databases start at 31513:
dbccalt
dbccdb
sybsecurity
sybsystemdb
sybsystemprocs
If you drop and recreate these databases after an upgrade, ASE applies these new dbids. The dbids for all other databases are determined in the same way as in earlier versions.
If you perform an upgrade in place, that is, you upgrade without rebuilding your system, you should not see any change in dbid between versions. This is an issue only if your maintenance scripts use these IDs and you build a new system from scratch, which will then use the new ID conventions.