Re-issue, CD, SACD, Tape....LP....and what studio tapes are being used....

Good luck with that. With the exception of a handful of audiophile labels on LP, a lot of labels are not transparent about source, let alone a so-called first generation master tape. I know the tape heads here will say they have a connection and get some stuff that’s not at a large remove, but most multitrack once mixed down to stereo is already a generation removed, no? Direct to disc is fab but it’s largely banal fare (yes, there are exceptions).
I’m not doing streaming (nothing against it, just have more music than I can already handle) and often wonder- what "master" does a given streaming service use?
At least with older LPs, there is lore, anecdotal info, you can sit with a pile of copies if you are industrious and decide for yourself. In some cases, the records I’m buying were only released in limited quantity, private label, and tapes are MIA.
I did check with one of the 800lb gorilla labels and they indeed had the "masters" for a label they bought as part of a big acquisition years ago. I was shocked. The records have been reissued in some cases, but the original pressings are the most desirable, sonically and marketwise.
What’s a mother to do? :)
We just consumers unless you producing....

@bdp24 - fair point on the use of "safety" copies. These days, trying to get access to the old tapes is very difficult unless you are Chad, Kevin Gray or someone within the fold. 
KOB has a huge amount written about it-- I think Sony (formerly CBS) retimed it in 1992, but the Classic LP was probably the first on vinyl after that correction was made. I gather from a friend who has done the comparisons that his best sounding copy, among many others, is a WLP mono- very early. I don't have one since I'm not really set up for mono.
As to Classic, Hobson did a lot to keep the format going in the dark days-I do find the Classics to sound a little tipped up but that's the nature of modern mastering. I bought most of the Classics I have (including a copy of KOB) at normal retail prices (read: cheap) at the time they were released. His 200 gram, flat profile effort resulted in some known QC problems, and the need for such thick vinyl is, in my estimation, questionable. (Yes, I have some old copies of records that are "heavy" but that's far from important in my listening experience- I also have records that are thinner than Dynaflex that also sound great).
My interests lead me to a lot of records that were never reissued or if they were, only by questionable sources. Thus, the need to bin dive (or Internet search, which is largely the way I buy relatively rare records, except for the occasional record show or trading among friends who are collectors/dealers). 
There are so many records out there from the pre-digital era that I could live a rich musical life without the need to buy any "new" LPs. Thankfully, some of the material that is being released today is decent--Roy Brooks' "Understanding" was recently released from old tapes-- not crazy money (though limited quantities). I've been captivated by Alice Coltrane's Ptah, which as far as I know, has not seen a reissue on vinyl since 1974. I don't know what the status of the tapes is since she is listed among those artists whose material was lost in the Uni-fire. 
I guess my main point is not to get totally locked into the audiophile approved stuff from the usual suspects only because it is siloed to what sells-- and there is a ton of music out there to be explored beyond the standard warhorses. (Yes, KOB is important, but there's a lot of very cool jazz from the early '70s that is well worth exploring, with killer players). My biggest gripe is the inflation in pricing as well as grading.