Believe me, beta-testing is more difficult than you think. I have beta-tested a hl2 mod.
1. Different computers get different bugs. I can understand that the PCs on the office are all the same model.
2. You don't really know if something is intentional or not.
3. You gotta be lucky to notice it when it happens.

Anyway, I have had a disaster happen to me. I married off an uncle to a duchess as duke of connacht(1081 start). The uncle went to a scottish duchy. The scottish king thought:"Hey, I can finally send my kilted crazies against some poor guy again!". And this way, I was left with one little county I just conquered the year before