When new subdistricts are created, the villages (muban) which form the new subdistrict are not assigned in a random order. In the many announcements I have processed so far, one system I noticed relatively often is the attempt to minimize the number of villages which change their number. Maybe the most striking example for this is the creation of Kham Phai (ตำบลคำไผ่), Loeng Nok Tha district in Ubon Ratchathani (now in Thai Charoen of Yasothon province, since the subdistrict experienced the creation if a new province in 1972 and a new district in 1992). This one was created in 1951 (Gazette) by splitting 19 villages from Som Pho subdistrict. Most of these villages kept their number - for example village 3 of Som Pho became village 3 of Kham Phai. In fact, only village 1 and 2, 10 and 11 and 17 till 19 of Kham Phai did have different numbers before.
While this system is relatively common, it by no means was the rule, there are also many announcement were the villages got new numbers even though it would have been possible to resort them another way to make some village keep their number. And of course there were also many cases where it wasn't possible to do such at all, as all the villages split off had numbers higher than the highest number in the new subdistrict. Or, to say it with numbers, out of the 22168 villages reassigned since 1950, 3422 or 15.4% kept their number. Also interesting - while in the 1990s the percentage was 24, and the rate goes down when going further into the past. In the 1950s it was just 7.5% which kept number.