Are you sure you had at least 75 nights every year? I have seen many posts here in FT stating that Marriott kept them at Plat even though they didn't get their full 75 nights.

When Marriott merged all their various programs (Marquis, CY Club, FFI Club, etc) they did not pull through the nights stayed in the non-Marquis programs. I probably had a couple hundred nights in CYs and was a CY Club Gold member for a number of years, but none of those nights came through.