The relevant paragraph on the TAO reads as follows:
The tambon administrative organization has as its legislative body a council composed of the kamnan and all village headmen, plus one elected member from each village. These councils receive appropriations from the Department of Local Administration through the budget of the provincial council, and from the Department of Community Development (CD) through the Provincial CD Officer. Since its inception in 1956, the tambon administrative organizations has remained lightly financed and heavily dependent upon grants-in-aid from the central government; the typical tambon council received a grant of only 10,000 baht (US$500) a year.Compare these with the current TAO council, which also has two representatives from each village, but the central administrative officers - subdistrict and village headmen - are no longer part of this council. When the TAO were created again since 1994, only in the first term of the councils the headmen were members of the council, but after this grace period the council has become completely elected.
Oddly, the above described TAO council in the 1960s is identical with the Tambon Councils as defined by the TAO and Tambon council act of 1994\, only that in 2001 the last of the Tambon councils were upgraded to TAO. If I am not mistaken, before 1994 these councils also included the subdistrict doctor, another official on the payroll of the Ministry of Interior. Guess I still have to research these two councils and their development a bit more to get the full picture.