But the rest of each episode was remastered--going back to the original 35 mm film negatives instead of relying on the digital copies that were made for the earlier DVDs.
"Digital copies"? I was under the impression, that the original 35mm negative duplicates were scanned in HD resolution but merely "down-rezed" for the first TOS DVD releases. If memory serves the TOS DVDs were advertised to come from freshly made and new (HD) masters.
Put simply, the TOS DVD owners already have the same original content as the TOS Blu-ray owners, although with less resolution / picture detail and color fidelity (because of DVD's MPEG-2 data compression).
Maxwell Everett probably has all the vital information on this subject.