Remember, the boardis non-executive. Which means their only formal contact with the club is when they get together once a month or so for a board meeting and are presented to by the executive. It is up to the executive (ie full time employees) to brief the board and fully disclose to them what's going on. Board meeting minutes will outline what has been discussed at board meetings and will be key to who was complicit.
I dunno whether I'm naive, but your white collar corporate types (eg chapman) take matters of ethics pretty seriously. I have no reason to question him at this point.
I'd say the only naive part (and I'm not attacking you by the way) is to think the directors only ever come across information about the club at board meetings, especially in a place like Adelaide AND involving the Crows. Unfortunately I have seen how ethical some members of the Crows board have been elsewhere (including Chapman) so I do not have any faith that in this instance they are telling the truth (they might well be). For instance, if the board did only hear about this for the first time last week, why the hell wasn't Trigg given the sack immediately? Seems like they are using this time to get all their stories straight maybe. Otherwise surely that type of deception requires instant dismissal, or force Trigg to step down.