When I was checking the website of Mae O subdistrict administrative organization (องค์การบริหารส่วนตำบลแม่อ้อ) in Chiang Rai, I found that unlike most websites of local government units they not only present their current personnel, but also the past chairmen of the TAO were listed on a separate page. Starting with the chairman of the Tambon Council (ประธานสภาตำบล), who was ex officio also the subdistrict headman, two more chairmen elected by the council (ประธานกรรมการบริหารองค์การบริหารส่วนตำบล) and since 2002 the directly elected chairmen (นายกองค์การบริหารส่วนตำบล). Sadly there's no explanation for the more than one year without any office holder from 2004 to 2006. Anyway, such complete lists of office holders are rare to find, and even more rare the past TAO council chairmen or the TAO clerks are lists.
But even more interesting is the history page, which is in fact the history of the subdistrict and not just of the TAO. And here all the previous subdistrict headmen are also listed. The notable part is the title given for the headmen before 1978 (until headmen number 10), which are listed as Pho Khwaen (พ่อแคว่น), literally "father of land/region". I guess it was only the local name for the headman, who still officially had the title "Kamnan", as already back in 1908 the names for the subdivisions and their leader were consolidated. Before that year, in the north the subdistricts were named Khwaen, and the headmen Nai Khwaen (นายแคว้น). As the table was reconstructed and the compiler did not know the years for the headmen before 1974, the title Pho Khwaen might also be simply due to the fact that the compile did not remember when the title Kamnan became official.