I'm not an expert by any means but don't masters (or some intermediate step; I don't know the nomenclature) based upon the original negatives from the OT-period exist that could be used as the basis of at least a remastered DVD release? I could see the resolution not being up to snuff for a Blu-Ray release but I'd be satisfied with anamorphically encoded DVD's.

Lacking that, wasn't the negative for each film scanned during/prior to 1997 so that all the SE work could commence?

Even if the negatives really have been altered, I find it hard to believe that the originals don't exist on a hard drive or as dupe or master or whatever the terms are.