In the census of 1920, immediately after Greece’s occupation of the “New Territories” the government of the day offers some revealing information. In the census of 19 December, 1920, the official Greek census form had a separate area asking: “what is your mother tongue? What is the language you speak at home? If your mother tongue is not Greek do you understand Greek?” This census document can be found in the book by M. Houliarakis (Geografiki, dioikitiki kai plithismiaki ekseliksi tis Ellados tom G’ page 363)
The data obtained from the census of 1920 offers great detail about the population to the point of distinguishing between deaf males and deaf females. It also includes the data on language and mother tongue.
Unfortunately, the census information relating to the population of the “New Territories” was never made public. This information preceded the exchanges of Christian and Muslim populations between Turkey and Greece or the so-called “voluntary” population exchanges between Greece and Bulgaria.
At that time Greece only published the results from the geographic area of “old Greece” (Sterea, Evoia, Thessalia, Arta, Ionian Islands, Cyclades, Peloponese…). Five volumes containing census data from the “New Territories,” which included information on religion and language, were prohibited from being made public.
In the archives of the Census Council or the General Archives of the Greek state we shall not find census data on the northern territories (the new territories of Macedonia and Western Thrace) for the census period of 1920.
However, page 182 of the volume of census data for 1920 (published in 1929) for the area of Trikala (in Thessaly and Arta just south of the new territories) the following linguistic categories are reported for mother tongue:
Greek, Spanish, Romi, Koutsovlach, Albanian, Bulgarian, Serbian and 37 individuals from Trikala who declared their mother tongue as Macedonian.
This is official census data published by the Greek government wherein, not only is the Macedonian language documented by the census authority but it is rightly distinguished from Bulgarian and Serbian.
See for yourselves.
Here is a highlight of the census were the Macedonians are mentioned, thank you Voya!