BRMS Media and expiration dates

BRMS question:

I've got a couple tapes in my tape library that show an expiration
data of 4/20/05 and 4/25/05, yet they aren't expired.

They were both used for incremental daily backups using the same
backup control group and there's been a full backup since these were
done - (the full backup was done from a different backup control
group).  Each serial set on the tapes are expired.

The caveat may be that minor changes have been made to the backup
group - tweaking the omit list etc - that may be causing some objects
on these backups to not appear on the fulls.

Is this my problem?  Will I have to manually expire tapes if I tweak
the omit list, or delete a library, or an IFS directory, will this
cause my tapes to not expire?

Thanks,

Rick