One of the strange features of TSM AD pool is that, when you do first incremental backup (for example 10 files), then change some data (for example 5 files) you’ll get incorrect number of files with query occupancy stg=adpool command. It will show you number of files equal to 15, the same as in your primary storage pool. But if you compare sizes of pool you’ll see a difference. So do not rely only on file number in your AD storage pool.