Ok,
So it feels like it's been in front of me the whole time, but Lucas has said that a high quality print of the original films before the SE's doesn't exist to be able to release the OT in a high quality format.
But surely when he took the original prints he had used to be restored for the SE's, they were committed to digital files in a computer to be able to do all the SE's tweaks and fixes.
So it stands to reason that there DOES exist a high definition cleaned up digital backup of all three OT films.
Or did he delete them as he was tweaking them?