Heirloom Yogurts? Yonah Schimmel Yogurt?

[Paulzie67]

Hey... Watched a video with Sandor Katz where the Yonah Schimmel yogurt was mentioned. I then started down the rabbit hole of trying to read and learn about Yonah Schimmels yogurt and other "heirloom" yogurts. I even sent a friend (that lives Near the Knishery) to go buy me some but they no longer make it!
So, My question(s):
Do "heirloom" yogurts have some rare type of microbial composition? Some rare species or subspecies perhaps? Some Unique combination that have evolved over generations and can no longer be replicated?
I was also wondering if anyone had ever even Tested the Yonah Schimmel yogurt or any heirloom variety to learn what strains are in them? I can find nothing online... Other than back in the early 1900's when Stamen Grigorov named L. bulgaricus?

IF So, Does anyone have Any of these rare heirloom yogurt starters?
Sandor Katz stated he got a yogurt that someone spread on a cloth for him and he kept it for 6 months or so before using them and made Great Yogurt for quite a while.
If they're so different or are better than any other newer starters, is anyone willing to share one dried on a cloth or parchment?
I'd love to try one!
TIA