The national wildlife authorities/FWS/First Nations management groups strategy is a bit similar to gene pool/founder stock strategies adopted with the Asiatic wild horse / Przewalski horse where there is an A-line and a B-line (one line with contribution of a domestic/Mongolian horse breed and one line without any of it).
You aren't quite correct about the modern day situation regarding Przewalski's horses, friend.
While
historically, yes, there were two subpopulations that were kept separate, that hasn't been the case since
2005 in American zoos. Longer still, for European zoos.
The Munich (U.S.) line was long upheld as the "pure" line. Although, amusingly, that almost certainly was never actually the case, given that one of the founders of it [18 (Bijsk 8), if you're curious] is now generally accepted as having been a Przewalski's/Domestic Horse hybrid. Lol.
And then to add insult to injury, genetic testing conducted in 2003 revealed that Askania Nova had
accidentally added in
more domesticated horse blood to the line!
You see, back in the 1970's, Askania Nova bred both Heck horses (Bred-back "Tarpans") & Przewalski's horses.
Via running them together as one herd during the breeding season!
Now, while Askania Nova had both sexes of P-Horse, they only had Heck horse
mares. So all of the Heck foals were being sired by P-Horse stallions. All well and good right? No Heck stallions around to sire "impure" foals on the P-Horse mares after all.
So, naturally, what happened instead was that Askania Nova staff lost track of what foals were purebreds, and which ones were crossbreds. The end result?
Multiple Przewalski's/Domestic Horse crosses being entered into the P-Horse studbook throughout the 1970's.
Thirty-something years was thought to be a little...
late to mix the mistakes that had been made when the truth finally came out, so I suspect that's why the zoo world seemed to just, collectively shrug it's shoulders. Given that the decision to merge the two P-Horse subpopulations together was quietly made afterwards and all, lol.
It just tickles me to death that the Old Prague line, long dismissed as being "impure" just because a
single Mongolian breed mare contributed to it [Via giving birth to a colt sired by a Przewalski's horse stallion. Said colt went on to sire a legacy of foals upon Przewalski's mares]... ended up having
less domesticated horse blood in it than the supposedly "pure" Munich (U.S.) line did!
I love irony.
("Purity" is overrated and "purebreeding" is an entirely human concept anyway. Animals are not particularly picky, and the species barrier is crossed not infrequently in nature.)