When is it too late to catch a revoke

So, if you've revoke but no one else notices, and you start the next hand, the previous result can no longer be changed. That is all.

I had: xx, KQT9, xx, AKxx. Against a good pair at the Atlanta club, Sean opened a canape 1D, I bid 1H, he bid 2H, I bid 4H. Dummy: Qx, Axxxx, QJTx, xx. LHO leads a high diamond spot. It goes A, K , 3rd diamond. I ruff with the K, draw trumps in 2 rounds, pitch a spade on the good diamond, lose a spade, ruff a spade, claim making 4. We played the next hand, after that hand, RHO begins wondering where the 13th diamond was. Apparently I had it the whole time and didn't even realize it, so we change the score to -100, which seems appropriate to me. Some discussion, not involving Sean or I takes place, rule books were consulted, and was determined that once they had bid the the following board, the previous one couldn't be adjusted.