I have mentioned my story before, but will do so again here.
I was matched as Marriott Gold after linking from Starwood (gold via Amex Platinum) when that became possible in early 2017. Shortly after that I decided to sign up for the 9 stay Platinum challenge with Marriott, figuring correctly that it would be rather painless with gold lounge access, etc. So, as of August 17th this year I had Platinum Status with Marriott through the end of 2018.
I was able to merge my accounts not long after the 18th, giving me roughly 60 combined nights. At first I showed as a regular Platinum member, but on its own the Marriott system upgraded that to PPE a few days later. I'm rather confused myself that if they did that for me automatically, how is it they didn't do it for all other Platinum-via-challenge?