That "on further investigation" could mean many things other than your presumptive interpretation that they accessed the account before they knew it was associa

That "on further investigation" could mean many things other than your presumptive interpretation that they accessed the account before they knew it was associated with Petraeus. For example, they could have suspected it was his, and then asked him for confirmation and access. At that point, he would have had to yield, due to his role, his prior agreements, and the situation (including the inevitability of access).