I'm at 8 years and 588 nights (combined) towards lifetime platinum in SPG and just called the SPG Platinum preferred line to ask how they would calculate lifetime platinum when they merge the accounts -- i will have another 100 nights from Marriott Rewards so will be above the 600-night threshhold but not sure if i'll have the 10 years or not given I never earned Platinum status at Marriott and only had a few years of MR Gold, which I'm not sure if i earned or if it was only because of United or a status match.
In any case, I will quote what i was told by the supervisor: Members need 10 years of combined elite status of Platinum Elite 50 night level or higher. 10-year renewal years do count as earned years for the sake of lifetime platinum status.
I have NO idea what that means -- the phrase Platinum Elite 50 night level or higher means nothing when applied to Marriott Rewards (since Platinum required 75 nights, and I have no clue with the second sentence means about renewal nights.
In addition when I called Marriott, they have no way to tell me how many nights I earned in a given year before 24 months ago, so no way to even figure out if i had 50 nights or more in any given year (if that in fact is the threshhold).
I'm not that concerned for me as worst case, I just need to qualify for Platinum this year and next and will get my LT status but it's super confusing.