Although Marriott says that activity history, SNA’s and free night certs on your old account take 72 hours to combine into your new combined account, in my experience it took 3 to 4 weeks for that to happen. Everything is now perfectly fine without any prompting from me.

My only peeve is that because I combined my SPG acct into my MR accnt, it now displays me as a member “since 2016” although with 10+ years as platinum.