BetaMAX, wow that takes me back my dad use to have a couple of those. They lost the video tape war to VHS(who else) even though betamax was far superior in quality.  Anyway.
Back to this cluster f.... BetaMax Just because nothing is written explaining the process used to encode back to 8 bit. Doesn't mean nothing was done. Why go into detail, the eps. are for my collection alone. I always look thru the 'unsorted' list and some other sources before fixing something that isnt actually broke. Re-encoding to keep my Archive the same and only when an alt. source can't be found.  Also I agree your 100% correct in saying that using a RAW would be the best choice to avoid "loss of quality".  I prefer not to mess with someone else encodes. But the number of sources still sharing have dropped to only a few.
       It wasnt too long ago, all of this wasn't even considered a possibility. Encodes from every type of media,(live,movies, TV,sports events, Anime) all had the same AVC 8bit video format. The rest are still the same and flourishing.  You can find 10 - 20 different versions of the same file. But not for an Anime, that doesnt happen anymore. The day something 10bit was posted. That was the start of everything going to shit, sharing fell into chaos and HEVC followed not long behind. The after effects have been worst case scenario. Most of the groups/sources from recent to those that had been sharing more than 10 years. That shared by Re-releasing their encodes etc.  Have quit and don't intend on ever sharing again. When asked, most reasons are the same.  
Just the other day I found encodes that were both 10bit and HEVC.