I've said it before and I'll say it again.
A suitable lifetime Titanium Elite status qualification criterion, competitive with Hilton and Hyatt, would be 1,000 Elite Qualifying Nights (EQN) and ten years as a Titanium Elite.
If Marriott information technology (IT) records are only reliable, with regard to the ten years, beginning in 2018, then that should be an explicit part of the terms and conditions.
Beaucoup Bonv∘y!