Even though these dogs were shown as early as 1884 and more in 1890, it was not enough to immediately become an official breed by the kennel clubs of America. As the end of the 19th century approached the dogs simply remained in a special class for breeds not recognized.
The time finally came, and in 1904, the very first Chihuahua was registered as number 2291 in the AKC stud book, under the name Midget. Midget's smooth coat was considered the norm since they were mostly thought of as terrier-type dogs. This was in contrast to the fact that many other varieties existed.
As the number of these early breeders increased, they seemed to be all in agreement that the variability in sizes, shapes, and coat lengths were hard to work with while perfecting show bloodlines.
Regardless, in 1923, with the founding of the American Chihuahua Club, the first breed standard was adopted. It clearly stated that the smooth coat and the long coat were two varieties of the same breed; nothing was different between them except for the coat.
Additionally, a standard size was determined. The new breed could not be over 6 pounds to qualify. Unfortunately, this was contrary to the average Chihuahua. Throughout time these dogs came in all sizes, from just a few pounds to as big as 10 pounds – a genetic characteristic that appears to go back nearly a thousand years.
This new size standard proved difficult for early breeders to control. It started a huge exodus to the West in search of smaller and smaller dogs for breeding.
Still to this day, size is something breeders struggle to control – it's just genetics and evolution at work. This is why many Chihuahuas start off small, but to the dismay of their owners, keep growing.