One thing to note is that you might not even realize sometimes you're getting a Platinum override when you are actually getting one. That's one thing I think Marriott should do (but obviously it's wayyyyyy down on the IT list) - have a pop-up showing the Platinum override was applied.

One way of finding out (or some don't realize) is because if they're logged in it will show availability to book (not necessarily at a cheap rate) but if not logged in it shows no availability.

Cheers.