On Crystal Isle, at the trench in desert, where the "Heir" versions should be
There are the "S" versions

They cant be tamed, wich is correct for the Heir's

But they don't act like the Heir should
* they are not aggressive
* They don't have the helmet
* they don't make nests (not 100% tested)

I've discovered that the way Vanilla Heir is spawned, is through several Graphs in the tamable vanilla version Base wyvern
Making it extremely confusing, both for me and others in the modding community :'(

So for now, I hope you can "live with" these flaws... they are not tamable, as they shouldn't (In the trench)
But every other in their naturel habitat is, and are the "S" version (My version) :)

I will continue working on it, and hopefully figure out something eventually ;)