Good info on the Sunderland token. It is indeed a bit odd, compared to the others. If I have read the Sunderland article correctly, the Northern General busses would do at least partially the same routes as the Sunderland busses. Both issued non-round tokens, but they were different in size and colour.
Wikipedia says Northern General expanded along the Newcastle-Gateshead-Chester-le-Street axis. Durham looks like a possibility at the outer edge only. Moreover, I can't imagine a token system for one school that is not even mentioned on the token, but I can easily imagine misreading how the school also used the tokens, so with all respect for Smith 2, I'll keep the mind open.
Peter