I heard directly from a reliable breeder who loves yorkies that they are almost impossible to house break.
My toy poodle on the other hand was housebroken in two days and never had an accident in the house.
When he got older I made sure he got out frequently but really he had admirable self control on those rare occasions where we had to leave him for a long time.
I think the secret is to get them out early and often so that they associate outside with going.
Smart, affectionate, good as gold - I did love that dog.