Dates of new subdivisions becoming effective

As it looks like Bueng Kan province will be created effective April 1, I noticed that this specific date is rather popular for new administrative entities. As there haven't been that many new provinces, a table of all the dates is relatively short.

• 1993-12-01: Amnat Charoen, Sa Kaeo, Nong Bua Lamphu
  
• 1982-09-27: Mukdahan
  
• 1977-08-28: Phayao
  
• 1972-03-01: Yasothon
  
• 1947-10-01: Kalasin
  
• 1946-05-10: Nakhon Nayok, Nonthaburi, Samut Prakan, Samut Sakhon
  

Provided I did not misunderstand the dates - for Phayao and Yasothon it said "one month after publication" so I assume same day in following month, there was none on April 1st. Note that the 1946 and 1947 provinces were in fact recreated after being abolished before.

However, when looking at the districts, April 1st is by far the most popular date. Since 1950, there were 410 newly created districts, most of them originally created as minor districts. Of these, 59 were effective April 1st, 14% of all districts. Other popular dates are May 1st (29 districts), July 1st (28 districts), July 15 (25 districts) and April 30 (21 districts). Only 11 districts were created on October 1st, the beginning of the fiscal year.

I don't know if the preferences of April 1st has to do with the fact that this date was the beginning of the Thai year until 1940. That date is also the anniversary of the Ministry of Interior, which started operation on April 1st 1892 with Prince Damrong as the first minister.