Here's an interesting one. My wife has a stay at Mandalay Bay on a conference rate for work. We booked 3 cheapo nights at Excalibur during the same time to get her to Titanium for our upcoming trip. The conference rate won't get anything for Marriot and isn't tied to anything so I assume there shouldn't be any issues having 2 reservations during the same time? I fully expect to have to fill out a missing stay request since we have to do it most of the time anyway but I'm just hoping they don't see the 2 reservations and give her grief.