The YTCA' history page goes into the original size of the breed and discusses the weight limit. From the start the cut off weight was 9lbs. That indicates that while there may have been some larger Yorkies at the time they were not eligible for the show ring.
YTCA mentions that many of the later day writers about the breed have never taken the time to do the proper research on the origin of the Yorkie.
http://www.ytca.org/history.html