I spend 125-150 nights a year at Marriott and have LT Titanium status (and current Ambassador status).
I doubt Marriott tracks people who assert the ultimate reservation guarantee, as its a local thing. I'm comfortable asserting the Ultimate Reservation Guarantee, 100 percent of the time it's covered. But ....with as many nights as I spend, its a once every 500 nights thing,. So unless you're having really bad luck, I wouldn't stress it.