to the o.p.
This is an age old subject that tends to get very heated and is very emotional for some yorkie owners. I also asked this question when i first joined and i was like WHOA what did i just ask??? lol
I read all the posts I could on the topic and drew my own conclusion
Thats really all you can do!
I went back to the very first yorkshire Terrier...read about him. Read about where the breed came from in the first place, and drew my conclusion from there. I dont think many genetics are on file from the very first mixture of dogs that made up the yorkie in the first place so to me seems hard to prove what came from what and what is in the to begin with
It is a very interesting topic when it doesnt get out of hand....Honestly as of today there is no for sure answer. There is speculation and some tests saying where they think it came from. Like someone said earlier these things can take decades.