In June 2005, the Election Commission announced the constituencies for three municipalities in Roi Et province. The first of these three was the subdistrict municipality Niwet (เทศบาลตำบลนิเวศน์) in Thawatburi district. Now the strange thing - this municipality was created in 2008 by upgrading the TAO Niwet. Did the election commission already draw the constituencies years before they were needed the first time? Normally, the constituency announcements come 60 to 100 days after the board meeting in which the upgrades were decided.
The issue cleared once I had all of the constituency announcements in my XML, and could thus check if there were municipalities where there was no corresponding municipality. It then turned out that I was missing the constituencies of Ban Niwet subdistrict municipality (เทศบาลตำบลบ้านนิเวศน์), a former sanitary district covering the central parts of Niwet subdistrict around the district office of Thawatburi district.
The list of villages (Muban) of the Niwet municipality omits the number 13, and since the above mentioned constituency definition defines the boundary by listing the villages everything clears up. This village is part of constituency 2, and since it is not part of the former TAO, the whole reason for the confusion was the fact that while writing the announcement someone accidentally left out the word "บ้าน" (Ban). The constituency definitions for Niwet municipality itself were published in 2008, shortly after the upgrade.