Bob, in any case he should talk to support. If the got corrupted DCBFs by appending to non-migrated media, he should also delete the DCBF related to the media just exported manually afterwards. I've seen several cases where this was required and the export did not removed the DCBF.
Right now, I struggle with a case where DCBFs get corrupted because of running sessions during the daily maintenance. If this is the case for him, he should talk to support. The indication for this would be an increasing count of DCBFs reported by omnidbutil -remap_dcdir from day to day. In that case omnidbcheck -media_consistency -fix might cause further issues by removing MPOS from the IDB. Not cool, so run this command with care.
Regards,
Sebastian