I’ve seen these upscales on Starz and they are very good. At least for the first season.
They could easily scan the same film masters and fill in the errors with the original broadcast tape and use the original audio to create a blu-ray release.
Rhino used original 35mm negative and some low contrast prints. They telecined them. Used DVNR to removed dirt and scratches. They backed them up to Digital Betacam. The resolution is obviously standard definition.