Most connect agents I know work following way( I just know ebu and
exchange, but rman might work the same):

While backing up an object (database), they are creating an unique
object in adsm and have it marked active. Active objects are reflecting
the actual state of the clients and are never deleted by automatic adsm
functions.

While the next backup occurs, changed files are backed up again and the
older backups are changed to inactive state. Now expiration processing
affects.

Connect agents have similar processing - but: objects are marked
inactive by the agent. This will work when you are deleting backup sets
with ebu. Now the adsm objects are marked inactive, expiration
processing occurs.

When you are using a value > 0 for verd, your objects are never deleted
in adsm, but are inaccessible from rman or ebu.

So it is needed to use the published values for expiration parameters,
because ebu has control about deletion of the backup files in adsm.

Regards Roger