Verify the volumes are beyond their expiration dates and are at "on site" locations.
Run the RBSRLSEXTP command to release them to the scratch pool.
Take a look at the at the "Automatic Release to Scratch" field for the Backup Class Entry for the sets/rotations in question. This field must be set to Y (YES) for these volumes to be released to the scratch pool with RBSRLSEXTP processing. If the volumes expire on the day RBSRLSEXTP is run, they release to scratch that day.