Hmm, sorry I cannot provide you any stories of my due diligence powers. I can only speak to the fact that I know my existing fiduciary duties don't make this an optional task.

I have a relative who works inside one of these large institutions and he has advised me multiple times: if we cannot verify what they're saying, you don't accept their investment -- it's as simple as that. The onus is on the investor to present themselves, and then the responsibility of accepting that investor in the group lies with management/ownership/board as designated by the corporation. Basically, you accept it or you don't.

A complex environment simply doesn't absolve me of my duties to my board.