"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."
From:
History of the Yorkshire Terrier by Joan Gordon