Marriott hasn't yet gotten night credits incorrect for me as a result of a post-midnight arrival--perhaps just good fortune, but I do believe keeping them informed made the difference. I've arrived after midnight many times, but do always contact the hotel in advance to let them know I'm definitely coming. On the occasions flight delays/mis-connections have made post-midnight arrival possible or likely, I also always communicate this to the hotel directly.

It may also be that Platinum status helped, but I don't really know: on the one occasion 6 years ago when I got "walked" after showing around 2:30 AM at a full-service Marriott the FDC was very upset by it; they knew they'd dropped the ball and the night manager got me a room at another Marriott about 10 minutes away in less than 5 minutes. I got the impression that if Marriott "sold" a room to a Platinum it was theirs whether they showed or not (due to the Ultimate Reservation Guarantee); they charge you the rate you booked and the taxes if you no-show, so may not want to risk selling the room again and having you show up after that since they'd have to pay cash and points for failing to honor the reservation. In any case, that one posted correctly...