Even if Starriott doesn't have the data going way back, they would have a number of more recent years showing the OP's lifetime status. Shouldn't that be sufficient for the continuation of the equivalent lifetime status?
Of is Starriott auditing every lifetime status account to check that the person would have qualified under 2018 rules? I can't imagine that there are many who were grandfathered so long ago into lifetime status under special rules, so it's hard to explain why they're doing this unless there's a bigger problem with many people somehow getting lifetime status fraudulently. Is anyone aware that something like this has happened, perhaps with many sales of lifetime status on eBay, if there's even a way for someone to do that (although there must be a way for some sufficiently creative insider......).