If I’m not mistaken, what’s meant by “the unaltered versions don’t exist” is that the OCN was cut up to insert the '97SE shots into it, right? So a full, intact copy of the original negative might not exist, but most of the OCN for the unaltered versions exists as part of the SE negative, and I imagine either the snipped portions still exist somewhere or complete prints of the unaltered versions exist that are only a generation or two removed from the OCN.

Basically what that means is that it’s not that the materials don’t exist to prepare a 4K restoration of the unaltered trilogy, but it would take some work to assemble the finished product from different materials - there’s no complete original negative they can just run through a scanner and be done with it.

So basically it’s not a question of whether they can, but whether they will.