Thanks, but I don't think that is it.

The system we are backing up has 16,841 MBytes in total, and the Audit
Occupancy shows:
        Normal system: 34,646 MBytes (so hardly two versions).
        RMAN system: 8,280 MBytes.
I am pretty certain that the DBA's implemented the delete old versions
correctly - because we stood over them while they did it.
The Q STGP shows the backup pool never goes over 87% full (total space is
136 GBytes). The databases we are backing up are about 180 MBytes.

Any further ideas I can check?


Cheers, Chris