I also re-qualified for Platinum by having 25 stays at legacy SPG hotels before the 18 August merger. However, like others have mentioned, my SPG/Marriott account still shows that I need X nights to requalify. I have emailed Marriott asking them to confirm that I will be Platinum Elite until 2020. I do have a screenshot of my SPG account with the 25 stays and text saying that I had requalified before the merger.