I spotted two file stored in the cpool totaling 23.5GB, which is about the same as the discrepancy between the pool size that BackupPC reports and what I'm counting on the file system.
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drwxr-x---. 130 backuppc backuppc 8.0K May 4 01:00 18
-rw-rw----. 1 backuppc backuppc 16G Apr 27 14:38 19524.1398.0
-rw-rw----. 1 backuppc backuppc 7.5G Apr 27 14:44 19524.1399.0
drwxr-x---. 130 backuppc backuppc 8.0K May 4 01:00 1a
drwxr-x---. 130 backuppc backuppc 8.0K May 4 01:00 1c
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