Truth is, I would say the vast majority of the good animals out there do not have a clear "line" any more. Now that in no way means that the vast majority of them are any less than they say they are... And for some that means that they should ask for more $$$ when that "line" does go back to the founding WC stock, and that is fair enough.... However, for me it just says that the buyer should beware and look at all the details they have on animals they choose to work with. And on top of that it would be easy for somebody to simply conform to this "line" idea by stretching some claim on an animal here and there.... which undermines the whole thing anyway.
Not really knowing either breeder myself I can not say if they did any mix-n-match breeding as far as these animals are concerned. But I know where you are coming from on your concerns. I remember some het for albino Mex-mex that were up for sale at some point... saw this idea once, it came and went, and I saw nothing more of it sense. The pictures looked like Mex-mex as far as I could tell, but never having seen a founding albino animal it did not feel right at all. The thing that stood out the most was the text with the add seemed a bit... well confrontational about them being legit without anybody prompting for that kind of defense.
All in all, for me this "line" thing has burned itself out now.
It probably does not matter anyway, after all what if the natural population of thayeri are a convergent population derived from Mex-mex and Ruthveni anyway? (or whatever you might think the melting pot is made with down that way) Truth is nobody really knows what a thayeri is for sure anyway. All we do know are a few localities animals were collected at decades ago, we even have huge gaps in the range we estimate they occur in.
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Herp Conservation Unlimited
If people really learn from their mistakes, I should be like the smartest guy in the world 
