The yorkie is a breed that goes through a number of changes as it grows. Unless you know the complete lineage and history of your pup, then it's difficult to say whether or not there's something else mixed in.
You know, I've read that some people suggest that even Biewer Yorkies were initially developed by another breed being mixed in. (Don't hollar at me Biewer owners!! I'm only repeating another's opinion.)
The most important thing is that you love your baby.
