I should have satisfied my Platinum Challenge with my last stay. When it was offered to me during an unrelated call, I was on the 2nd day of a 4-night stay and specifically told that the current stay would count since the Ts&Cs stated "stays completed within the 90 days". Customer Care is now walking this back to say that the 4-night I was in during registration doesn't count.
Registration for this challenge does not appear on my Promotions page, so I cannot see the exact Ts&Cs. Does anybody have a link to it or a screenshot?