ETA: Who sets the breed standards?
In the US, the official breed club writes the standards and the AKC accepts them. AKC I suppose could reject something but I don't know if that's ever happened.
Other countries, other registries, other breed clubs may operate differently.
From the current poodle breed standard as accepted by AKC:
The Toy Poodle is 10 inches or under at the highest point of the shoulders. Any Poodle which is more than 10 inches at the highest point of the shoulders shall be disqualified from competition as a Toy Poodle.
As long as the Toy Poodle is definitely a Toy Poodle, and the Miniature Poodle a Miniature Poodle, both in balance and proportion for the Variety, diminutiveness shall be the deciding factor when all other points are equal.
(I'm still trying to decipher what this means. Deciding factor in what? Help!)
The height (and even weight for some time) has varied from registry to registry since the clubs began to be formed in the late 1800's.
There's also been some deliberate crossing by breeders in the US and outside at times to improve certain traits so the toys going oversize have historical genetics behind them.
The Kennel Club (UK) current toy standard
Poodles (toy): height at shoulder should be under 28 cms (11 ins).
This makes their miniature
Poodles (Miniature): height at shoulder should be under 38 cms (15 ins) but not under 28 cms (11 ins).
Standard poodles have no upper limit here.
I read somewhere that I've not found again that Standard poodles were averaging closer to 20-21" at the turn of the 20th century. If that's true then standards have been slowly bred bigger which could explain part of the wide gap from miniatures of any registry not including the FCI medium to standards in real life.
The Poodle Club (1886)
The Toy Poodle should resemble the Poodle in every respect except:
Coat: often softer and silky.
Height: under 12 inches.
Weight: under 10 pounds.
Standard published in the United States in 1901
Weight limits: The weights are divided into sizes, viz: Large size, over 40 pounds. Medium size, over 20 pounds to 40 pounds inclusive. Small size, 20 pounds or under.
Standard set by The Poodle Club in England in 1886 and published in the United States in 1905
The Toy Poodle: The Toy Poodle should resemble the Poodle in every respect except: Coat: often softer and silky. Height: under 12 inches. Weight: under 10 pounds. (This was added in 1905 in U.S.)
Standard published in the United States in 1916 is identical except:
The Toy Poodle: is all white. The Toy should not exceed 12 inches at the shoulder, be not over 10 pounds, and be a miniature of the full-sized dog. The coat must be very profuse and of a soft silky nature.
Standard published by The American Kennel Club in the first edition of Pure-Bred dogs in 1929
Weight: Miniature 12 to 20 pounds; large over 20 pounds.
Standard for Poodles as approved 1959
The Board of Directors of The American Kennel Club
11. Size
The Standard Poodle is over 15 inches at the withers. Any Poodle which is 15 inches or less in height shall be disqalified from competition as a Standard Poodle.
The Miniature Poodle is 15 inches or under at the withers, with a minimum height in excess of 10 inches. Any Poodle which is over 15 inches or 10 inches or less at the withers shall be disqualified from competition as a Miniature Poodle.
The Toy Poodle is 10 inches or under at the withers. Any Poodle which is more than 10 inches at the withers shall be disqualified from competition as a Toy Poodle.
PBSTD5 (archive.org)
These are first hand articles written by some well known breeders about some history from the turn of the 20th century to the mid-late 1930's. Iv'e never gotten around to putting them together to see if or how the first hand accounts tally with these few examples of breed standards.
Articles from the 1930's by Alice Lang Rogers (Mrs. Byron Rogers; Misty Isles) and Hayes Blake Hoyt (Blakeen), and others.
Alice Lang Rogers, The Miniature Poodle: Glimpses Past and Future (Mrs. Rogers was AKC Gazette Poodle columnist during the later 1930's; this may come from the Gazette, 1937.)
"In the year 1905 the English Kennel Club separated Miniature Poodles from the Standards and put the former on the toy dog register. This proved to be so detrimental to the breed that in 1924 the governing body took them out of the toy section, and, while keeping them as a distinct variety with separate championships, the interbreeding between them and the Standard again became legal.
"As everyone knows, it was from the small or medium Standard Poodle that Miniatures were evolved, so in all pedigrees we go back, many generations ago, to well known dogs of the large variety. In England, still today, puppies are not eligible to compete in Miniature classification; this clause was put in during those early days as a safeguard against an immature Standard Poodle winning as Miniature in its youth and later growing to large Poodle size.
"It was not until 1933 that Miniature Poodles were given a separate classification in this country. Previous to this time, they were shown in the Toy Poodle section,
In spite of the fact that in this year the AKC gave the Miniatures their own classes they are still looked upon here as merely a variety of Standard Poodles, and today any Poodle weighing less than 12 pounds may be registered and shown as a Toy Poodle.
"Quite recently we have taken a big step in advance; the AKC has agreed to allow a class for specials only in the Miniature variety as distinct from the Standards, and the supporters of the little fellows are very much elated.
"When one remembers that only four years have elapsed since we had our first recognition as a distinct variety [by which we infer date of publication: 1937], we need not despair; and our next hope is that we shall be granted the right to Stud Book registrations under our own title and our own place in the non-sporting division as a separate breed, not merely as an off-shoot of the Standards.
"More and more, too, do we find judges looking for Poodle type over mere diminutiveness, and this is a step in the right direction. Far be it from me to sponsor the 15-inch Miniature, but we must have substance, good quarters and "big-littleness"
Our greatest selling point just now is that we can offer a really typical Poodle in small bulk, but our market does not, and should not, come from the people who are looking for a Toy dog in any sense of the word. For this reason a good many people really prefer, as a pet, the Miniature which, strictly speaking we would feel unwilling to bench on account of a possible 14-3/4 inches of height. This gives us a ready market for our occasional big fellows - and beautiful Poodles they are as a rule. As our breeding operations progress we will of course produce fewer and fewer of the over-14-inch dogs (if we breed successfully that is) because each generation properly mated will have less and less hereditary tendency to size.
Hayes Blake Hoyt, "Poodles Across the Pond" (Popular Dogs, 1937)
I would say that the American Standard surpasses its English cousin in head and feet, but that the English Poodle is still ahead of us in size and coat. The English coats, as a rule, are magnificent, of the right texture and quality and absolutely free of mats. The size of the English Standard Poodles is truly astonishing, as most of the winning dogs in England are very large-boned and considerably bigger than our winning dogs here. The Miniatures, as a whole, are rather better than most of ours, and here again the English prefer the larger Miniature to the very small one; that is, a Miniature right up to 14-1/2 inches rather than 10 or 12 inches!
Andress (archive.org)
Genetic Diversity Testing for Toy Poodles (VGL UCDavis)
There is a theory that Maltese or Havanese may have been crossed to poodles prior to the 1800’s to produce Toy Poodles as suggested by the silky coats found in early toys.1 The present DNAbased study also boosts this theory. The first Toy Poodles depicted in Europe were usually white or white with markings and used to hunt truffles or act as companions. Small white toys from the European continent are thought to have been the foundation for the breed in both the UK and the US. Toy Poodles (which were white) were established as a breed in the United States as far back as 1896 and the first Toy champion was recorded in 1910. Shortly after that time Toy Poodles were accepted as a breed by the AKC, separate from other Poodles. These early Toys were small (3.5 to 5 lbs.) and did not have the same type as the Miniature and Standard Poodles. The breed standard proposed by the International Toy Poodle Club in Philadelphia was published by the AKC in the official book of breed standards in 1929 and had a required weight maximum of 12 pounds. A height maximum of 10 inches was added subsequently to prevent larger dogs from dominating in shows1 .
According to Mackey Irick (“The New Poodle”, 1986),1 many US Toy Poodles can be traced back to CH Happy Chappy, born in 1932 bred by Florence Orsie. Happy Chappy is also the sire of the first colored Toy champion, a silver produced by breeding him to a silver miniature. In 1940, registration papers were revoked for these inter-variety offspring with the argument that these dogs were not true Toy Poodles. Research presented by EE. Ferguson to the AKC resulted in a reversal of this decision, and Toy Poodles were placed within the Poodle breed as a size variety instead of as a separate breed in 1943. Between the 1940s and the 1980s many Toy to Miniature crosses were done to try to improve the type of the existing Toy Poodles and add new colors. This type of breeding continued until the 1970’s or 1980’s, after which most breeding was kept mainly within the variety and within colors1 . Although the result of crossing the original Toys to Miniatures improved head, length of leg, length of body, and coat, it has made it difficult to produce well typed dogs within the desired height of 9.5 to 10 inches at the shoulder. The height issue continues to be one of the biggest challenges for breeders2 .
ToyPoodle20191010.pdf (ucdavis.edu)
Dogs of all nations : Mason, Walter Esplin, 1867- : Free Download, Borrow, and Streaming : Internet Archive
published 1915
I'd love to find more on the history of all these changes and see how they've brought poodles to where they are now.