It is first of all necessary to go up in time and to understand that the "fashion" always had an important impact on the physical transformations of a race of cat. Just like the Persan one which did not have a nose as flat as now.
The fashion of years 60-70 was the appreciation of the lines to the extreme. What made disapeared the old-style Siamese in the cat-show world, but also near the breeders. This was the consequence of the constraints of the time or quite simply by defeatism. Fortunately, certain breeders persisted and continued the breeding of the Siamese of the origin.
This selected breed of Siamese met a frank success. The name of SIAMESE remained, and henceforth anchored to the new forms, long-limbed and very slender. One speaks then about an evolution of the race, as well as we continue to speak about Persan "transformed" with his nose, currently, completely flat.
It thus been necessary to find a name for the old-style Siamese, with the rounder forms and of squater aspect. The name of "THAI" was found to him, since originating in Thailand.
However, small historical background, the Siamese comes from Siam, Kingdom of Siam, we already said it, and its traces go up until XIV th century. The coup d'etat of June 24, 1932 in Siam is a transition without bloodshed from an absolute monarchy to a constitutional monarchy. One changed the name of the country, which of Siam becomes Prathet Thai, "country of the Thais" or Thailand. This name implied a unit of all the people of language Thai. Another argument is etymological, the word thai also meaning "free" . The name of Prathet Thai initially is employed not officially between 1939 and 1945 then declared official on May 11, 1949.
Then, why had there modification of the name of the breed of a cat whose origins are clearly proven, and anchored in a population, whereas the "extreme" type is a pure fabrication and handling of the man ? Or is this a pure selection made by the man, who with in my opinion went too far ! ........
Evolution of time, evolution of manners, evolution of the breed.........
It is important to note that in the popular speech, "Siamese" is a squat cat, tubby with the round head. And not, of slender and slim form, such as one currently sees them in cat-show.
Moreover, before the transition from the Siamese term towards the Thai term, there exists on old pedigrees (in Belgium), the term " SIAMOIS THAÏ " (SIAMESE THAI). Not leaving any ambiguity on the morphology of the cat concerned. Certain breeders refused besides to qualify their Siamese as Thai ; for this reason we also find in Belgium over the pedigrees, the Siamese term, but this time, qualifying the traditional Siamese, the therefore round one. It acts of a return to the sources, by a refusal of the evolution of manners and habits.
American club PREOSSIA was the first to use term "OLD-STYLE" in order to officially define the name Siamese of an Old Type. In England, year 2000, was founded club OSSC, and used also this terminology.
The term " ANCIEN " (OLD) was also introduced in France, in order to differentiate it from Siamese, but also from Thai (see what it at the present time occurs to FRANCE).......
The term "TRADITIONAL" is a little total term, used in all the countries. It refers to Siamese of the origin, known in Siam and imported into England in end of the XIX th century.
And finally, one sees also the name " SIAMOIS DE NOS GRAND-MERES " ( SIAMESE OF OUR GRAND-MOTHERS). This called upon the morphology of Siamese before transformation, therefore about the years 1950-1960.
Of average size, the Thai must remain rustic like Siamese of our grandmothers. What makes the difference with the Siamese current one, it is especially the head which triangular but with angles is rounded and strong cheeks from where its name of "SIAMOIS A TETE RONDE " ( SIAMESE WITH ROUND HEAD = APPLE HEAD).