[James2001]

It does depend on if the film inserts still exist to be rescanned in HD though, in many cases they don't. I know when it came to the Monty Python Blu-Ray, only a handful of the live action film inserts still existed (Terry Gilliam had kept hold of the animations though).

OFAH have released a Blu-Ray of the 1985-89 Christmas specials (which includes the uncut Royal Flush in addition to the terrible edit that ended up on DVD), and while I haven't bought it, from what I've read, the Frog's Legacy is entirely upscaled SD, even the film sequences, so presumably the film no longer exists.

Though many of these 70s and 80s telecine transfers were so poor that even just a rescan in SD would probably be massive improvement. It's amazing how blurry many of them are, and how much dirt and scratches there are on the film.

---

The advantage of Blu-ray isn't higher resolution in these cases, it's the ability to have more content on a single disc. What would be a six disc box set on DVD could be two discs on Blu-Ray.

Resolution is only one part of the equation when it comes to picture quality. MPEG1/2 compression is 25-30 year old technology at this point and is lossy; liable to introduce visible artefacts which would not be present on an upscaled Blu-ray.

Doesn't even need to be upscaled, you can have SD content on Blu-Ray, and with better codecs and higher bitrates than DVD (MPEG-2 up to 15mbps I believe, when DVD peaks out at 9.8mbps, and most DVDs won't get anywhere near that, and H.264 up to 12mbps, I think, not to mention the better choice of audio codecs, including lossless). Certainly in some countries they release Blu-Rays of (non-upscaled) SD shows and you can get 20 or more episodes on a disc at the same or better quality than DVD.