[Meggie]

One of my old ones used to weigh 12lb.
It isn't unusual to get the larger ones, you see quite a few around as pets. Not surprising really when you consider the breeds that the Yorkie was developed from, the Paisley & the Clydesdale were both biggish terriers & the Skye is one of the biggest. I have Skye terriers as well as Yorkies & the Skyes are very heavy, 35-40lb ish, big dogs on short legs.
Yorkies were bred down from these larger breeds.

So all lines can throw bigger puppies, even if you mate a small dog to a small bitch there's no guarantee that all the puppies will be tiny, you can easily get throw backs.After all, the Yorkie is a relatively new breed, having only evolved in the late 19th century, when you compare it to some of the other breeds that go back hundreds of years & have had much longer to fix the type.
Some of the early famous Yorkies that were shown in England as late as the 1920s were well above the current show weight.