When I was first looking for the old census data, one of the online resource I found was the Open Data library of the Worldbank, which includes some documents from the 1970 census. Though not the actual census data - which I later got elsewhere - but also the codebook is an interesting resource as it contains a list of the provinces with the number of districts, subdistrict and administrative villages, and even more useful a list of all the subdistricts with their village numbers - the total numbers for 1970 were 580 districts (including the minor districts), 5126 subdistricts and 45504 villages.
I am slowly working through this document to extract all these village numbers and compile them in my XML structure, which already turned out to be a good cross-check of the data I already compiled as I found a few cases where I had missed or wrongly added the creation of a subdistrict. The document however has two drawbacks, some pages are badly printed and even have hand-written corrections making the numbers sometimes difficult or impossible to read. The Thai names seem to have mistakes sometimes as well, some might have been spelling changes however which were not announced in the Royal Gazette. Also, some pages are missing, so it cannot be turned into a complete 1970 subdistrict list.
Ban Chang (ตำบลบ้านฉาง) - and instead the list shows a Ban Nao subdistrict (ตำบลบ้านนาว) with seven Muban. As there are zero Google hits for such a subdistrict name, and I the name of Ban Chang seemed to have never changed, it might have been a mistake in the Thai name, changing two characters. But - Ban Chang has just four villages, but Ban Nao had seven, and there was no change in the boundaries of Ban Chang either explaining how the village number could have decreased. I can only suspect this is a real mistake in the codebook.
Issues of the Local Directory (ทำเนียบท้องที่) from about that time would help to clear up this issue as well as help to fill the pages missing in that file, but none of these are available online, and those few libraries I could visit so far in Thailand didn't have any such books.