I’ve traveled down this research path for a little while now and as far as I can tell it essentially boils down to this:
The original video masters existed in a variety of masters tweaked and untweaked starting with the initial VHS and LD releases here in the US from 16mm sources. In Japan they got the big Log boxsets that added PCM mono but appear to be ports of the same USA LD masters otherwise and they all have apparently Season 3 opening credits. Some claim the Japanese LDs have spiffed up transfers and other say the opposite. In my experience most Japanese LDs do port US picture masters.
For the first DVDs of the two episodes per disc they went back to the existing masters and brought them into the digital realm-and also upmixed the original mono to 5.1. They also have 2.0 tracks but sadly these are not mono but Dolby surround versions of the 5.1 upmix. I thought I would have to track these down for a mostly untouched TOS but apparently the main plastic shell 2004 DVD set reused these disc masters with better bitrate and encoding-representing the final release of the 16mm sourced video editions that closely resembled the original broadcast appearance-albeit without the original mono.
When the remastered versions arrived on DVD and then HDDVD they lacked original audio and effects but were the first time we saw what the new scans and cleanups looked like. Finally the BDs arrived and added the original effects plus lossy mono but more clearly showed these were indeed 2006 era transfers riddled with DNR. That said they look very good and more like film-but they do look different to the earlier appearance and how the broadcast would have looked. The audio remix appears to have been done again with new effects and nowt like the original 5.1 on first dvds which merely spread around the mono.
The monos seem for the most part intact but you do notice some new effects here and there and some episodes have the new theme rerecording downmixed in mono for some reason. It is the first time since the final VHS run any form of mono is on a TOS release but infuriating they couldn’t just give us proper lossless mono and no DNR to make a definitive TOS BD release.
They really need to do it again and finally do it right.
I’ve often thought about getting the Japanese LD boxes but they are very expensive and I don’t know if the mono quality is worthwhile enough to justify the purchase. One could get the entire run on VHS on the 1994 blue spine ediiton for hifi mono but still the japanese pcm would be best overall. Has anyone been able to make a definitive list of all Blu-ray mono differences?