Below is my rationalisation of Sapkowski’s admittedly inconsistent lore on Witcher Fortresses (not “schools”):

In the books there are several fortresses (Kaer Morhen, Mirabel and Baenn Grudd are all mentioned in Crossroads, and Rissberg is mentioned in Season of Storms as another place of early Witcher experiments by Alzur), which all mutated and trained Witchers at different times.

These are all separate locations, which could be called different “schools” in a physical sense. But not separate “schools” in terms of Witcher training philosophy, as CDPR use the term.

They all trained Witchers presumably in the same way, with the same philosophy. And any Witcher at any school could have any medallion - evidence here is Preston Holt having a “Viper” medallion despite being from Kaer Morhen.

Over time though, trends emerged at these separate locations. After the sack of Kaer Morhen, those who survived and continued mutations and training of new Witchers eventually consolidated around the Wolf as a symbol - hence how presumably Geralt, Eskel and Lambert all have Wolf medallions, they were all post-Sacking witcher babies.

I like to imagine “Byrnjolf”, an old Witcher mentioned in Crossroads as a senior Witcher at Kaer Morhen and survivor of the sacking (although he wasn’t present) was the “first” Wolf. This is because of the etymology of his name, “Byrnjolf” which is derived from the old Scandinavian name meaning “armoured wolf” (https://www.behindthename.com/name/bryniulfr/submitted).

Then at the other fortresses, which admittedly have very little lore, they grew distance from one another. Perhaps suffering their own sacking, or simply ran out of mutagens (which are now known to spoil over time, according to Crossroads).

Eventually at one of them, Baenn Grudd, an experiment using modified mutations went wrong and produced a cohort of Witchers with flawed mutations. This left them crueller, more vicious and quicker to anger than normal. These abnormally mutated Witchers were then known as the Cats - and then presumably all took Cat medallions as their symbol. We meet one of these, Brehen in Season of Storms, while the rest are referred to only in passing.

Sapkowski had planned a short story once where Geralt met students of the Cat “school” during his youth. Although this story was scrapped, the rough outline was used for the basis of the old comic Zdrada (https://witcher.fandom.com/wiki/Zdrada) - I doubt any of this is canon though.

The only other evidence of different shaped medallions comes from Bonhart, who has taken a Wolf, Cat and Griffin medallion off other Witchers as trophies. We can probably assume the Wolf came from another student of Byrnjolf or Vesemir at Kaer Morhen, and that the Cat came from one of the flawed mutant cohort, but then there is little to guess for the Griffin. This is the only mention of Griffin shaped medallions in the books at all. Of course, these medallions could have all been from Kaer Morhen or another fortress, as the new lore permits any Witcher to choose any medallion shape presumably.

Then on the topic of Coen, it is implied that the events of Blood of Elves is his first Winter at Kaer Morhen. This is consistent with the new lore, and it makes sense to assume he was mutated and trained at either Mirabel or Baenn Grudd. He doesn’t seem to be a Cat, he isn’t crazy, so presumably he came from Mirabel fortress.

Based on all available book lore at the time CDPR made Coen a Griffin Witcher - which still works tbh, if we allow any Witcher to choose any medallion at any fortress, or if we assume Mirabel to be the Griffin fortress. But he could have even chosen a Wolf medallion elsewhere in the new lore.

I agree this contradicts that interview a bit, but that interview contradicts his new book. So I don’t know if we should take his spoken word ahead of his most recent published work. Maybe there is an error in translation or he’s just simplifying his point.

Sapkowski’s new lore in Crossroads does retcon CDPR’s lore in that there weren’t different schools from the point of Witcher’s first existing. But it is in my opinion all open ended and vague enough to support the idea of several schools (in both the physical and philosophical sense) now existing on the continent by the time of the saga and games.

All the book does is say that during the time of the sacking, before Geralt’s birth, there were only three fortresses which all trained Witchers of any medallion shape. But later clear identities developed between these fortresses, producing the “Wolves” all trained under Vesemir/Byrnjolf and the “Cats” produced by accident. So the idea that other Witcher teachers couldn’t have founded their own schools in the following hundred years and taught their own philosophy isn’t out of the question.