kev - I imagine any river record would have more stringent criteria than someone claiming they've caught a big fish. I've no reason to doubt The Tank either, and I guess that's the difference between an official record and an unofficial record.
I've caught a 13lber from the Goyt but know of two bigger fish claims 13lb 4oz and over 14lb from the same river. Yet the official record is Jerry's 12lb 8oz fish. Also Hobby caught a 12lb 12oz fish a few days ago....though, although I don't know which stretch it came from, it was caught after hours.
I doubt if Dave Mason will have any Tame stats; someone actually has to claim the record, to be on the official list.
If, like me, you mainly fish by yourself....you'll never be able to claim a record