On the website of the Department of Provincial Administration (DOPA) I finally found lists of all the Tambon Councils (สภาตำบล). As the subpages are not indexed by google, so it was more or less fluke I played with the image map of the index page and discovered the interesting stuff below.
The Tambon Councils (TC) are also a local administrative entity, however even lower than the subdistrict administration organizations (TAO), without any elected council and not a legal person. All the current TAOs were in fact created by upgrading the Tambon Councils. A few remained after the big wave of TAO creations 1996-1999, in fact those lists contain 214 entries for 2001 and 219 for 2000 and 1999. I already found announcements in the Royal Gazette by which a lot of TCs were merged into either municipalities or TAO in 2003 and 2004, but never knew if any TCs survived till today.
Thus by checking these lists of TCs with those announcements I had processed before, I could eliminate all but a just about 5 of them. It turned out that some I simply overlooked when translating the announcement into XML as I did not notice it were two TC simultaneously merged into one TAO or municipality. Another two I found in announcements I did not look at before as the title was different from the standard ones. It only leaves a single TC I cannot find anything about - Lamphu (สภาตำบลลำภู). But it seems that one was a quite peculiar one, because in the tables it has the comment "ไม่มีประชากร" (does not have population), not surprisingly as the whole subdistrict is part of the town Nong Bua Lamphu anyway. But the tables are not fully correct either, a few TC are mentioned in the 2004 announcements but not listed in the tables.
But in summary: The last Tambon Councils were abolished in 2004, since then it only has TAO and municipalities.