Prince Damrong on the thesaphiban reforms

The article Hegemony and resistance in northeastern Thailand by Charles F. Keyes (in: Regions and National Integration in Thailand, 1892-1992) starts by citing Prince Damrong, Minister of the Interior 1892-1915 and father of the thesaphiban administrative reforms. It was first published in 1935 in the book "Historical anecdotes" (นิทานโบราณคดี).

When the domains of the hinterland of the kingdom were organized into monthon in about 1890 in the fifth reign (i.e. the reign of King Chulalongkorn), the monthon containing the domains of the black-bellied Lao was first called "Monthon Chiang" (and those containing) the white-bellied Lao were called "Monthon Lao Phuan" and "Monthon Lao Kao". [...]
... and the names of the monthon were changed in accord with their directional location within the kingdom: Monthon Chiang became Monthon Phayap, Monthon Lao Phuan became Monthon Udon, and Monthon Lao Kao became Monthon Isan.

The directoral terms from the Sanskrit I mentioned before already. The previous names refer to the older principalities, Chiang Mai of course became Chiang, Phuan to Chiang Khwang (Xieng Khoung) and Kao to Luang Prabang. The black-bellied refers to the traditional tattoo on the bellies, whereas the white-bellied did not do like that.

However these names don't fit with the announcement in the Royal Gazette, which in 1899 announced the creation of the four Monthon and renamed them in 1901.

• Tawan Tok Chiang Nuea (ตวันตกเฉียงเหนือ) around Chiang Mai, later named Phayap (พายัพ)
• Fai Nuea (ฝ่ายเหนือ) around Khon Kaen, later named Udon (อุดร)
• Tawan Ok Chiang Nuea (ตวันออกเฉียงเหนือ) around Ubon Ratchathani, later named Isan (อีสาณ)
• Tawan Ok (ตวันออก) around Battambang, later named Burapha (บูรพา)