Doing some little research on how routes for buses (and other fixed-route transport) in Thailand is set and evolves over time. From my understanding so far, it kinda started with this PDF from 1954: https://ratchakitcha.soc.go.th/documents/1156537.pdf
commit 6cfb348
Here. That's the Transport Act B.E. 2497 (1954): §12 lets the committee set routes and how many operators get licensed, via Gazette notice. So the route announcements after it should show how routes changed. Want me to dig into those?