Here is a excerpt from an article on the YTCA website :
“Yorkshire Terriers were given their breed name by 1874, although it had been around since 1870. Originally they were known and shown as Broken Haired Scotch Terriers or Toy Terrier (rough and broken haired).
Almost all of the classes were divided by weight. The classes were for
Broken Haired or Rough Scotch Terriers less than 5 lbs. or 6 lbs. and under;
Toy Terriers 4 lbs. and under, or 5 lbs. not exceeding 7 lbs., or 6 lbs. and over; or Blue Scotch Terriers under 7 lbs. or 7 lbs. not exceeding 9 lbs. The largest weight class in which they were reported
to have been shown was for Broken Haired Scotch Terrier 9 lbs. not exceeding 12 lbs. This record should prove that although there were larger Yorkshires they were not being shown at the dog shows.
The record proves that the small size was available for breeding from early days.”
I know from my experience and a few other knowledgeable breeders that we can consistently produce healthy yorkies under 4 lbs.(not just an occasional small puppy). The reason we can do this is because we understand genetics, study the pedigrees of our yorkies, and the fact that small genetics already exists in the Yorkshire Terrier which is proven in the article on the YTCA website.
Attached is a picture of a 3 month old puppy of ours.

She came from a litter of four, 3 of the puppies will probably never make it to 2 lbs. And the fourth puppy may make it to 3 lbs. Not only are they all small but two of them (if they were larger) could be considered as show quality.
I have two questions:
1. Why is a breeder who breeds for small Yorkies not reputable?
2. If you breed for small yorkies how would you ethically describe your yorkies?