Thank you Lorry and DrJack54.
If anyone else has had a different experience (i.e. they demanded to see the TM.30 receipt otherwise no extension) this or last year at Chaengwattana then please let me know. It's quite far out to go there so I'm trying to prevent any repeat visits.
I wish I had taken a photo or made a copy of it, then I could've shown that. I never expected anyone to remove the paper receipt from my passport.
It makes sense if they could just check their database instead of demanding the paper receipt. However I had stayed at hotels around Thailand, so that would mean that the address in their system would now be different from my usual residence, which can be a problem for extension, right?
Or do you guys think they won't even check their database, i.e. they no longer care about TM.30 compliance at Chaengwattana? It'd be good if that's the situation now, as it was strict some years ago, and I had to pay 800 THB.