I don't think they overlooked it as much as they didn't think it would be an issue. Don't forget the Pats already let him interview for a GM once with Miami and there was no reason to think they wouldn't again. I think its just this year they have lost so many, gotten so much bad press and BB is several years older and Brady closer to retirement that they didn't think they could afford to lose him right now.
Also he has an agent, wouldn't it be his agent's job to know what's in the contract just as much as Caserio? Hell you can make an argument that its even more his job because that's what he's hired for. When I take my car to the mechanic I don't think its my job to understand why my car isn't working that's what I'm paying the mechanic for. Likewise I work in IT, I don't try to explain to someone why their computer isn't working, unless they ask, I just fix it and tell them what they can do to avoid the problem in the future.