FYI, was on the phone with a Marriott agent who was absolutely insistent that the legacy 25 stay requirement had to be met by the mid-August merger date, that's it's been the "new rules in place since then, and also insistent that he had read this on the Marriott Rewards website, yet invited me to call back or e-mail with anything from Marriott that would clarify that.
So, called back with the Terms & Conditions excerpt quoted above, spoke to a different agent who knew this as well, and was happy to notate my account accordingly "in case you get an agent like that again."