I am not saying you are wrong- only that we specifically asked about this today and we were told you could do both every entry. The guy could be wrong, the rules could change, this stuff is more art than science- but he was very explicit.
so it seems- I had stopped going to the one by the other government offices and was driving to Mae Sai instead, but decided to "do it the easy way" without knowing they moved. It's definitely not common knowledge yet as other people showed up while we were there and also assumed the holiday must be the reason.
turns out it's even simpler than this- the Chiang Rai office moved but didn't take down the signage or leave a note for dumb people like me. So the office I went to was closed AND it was a school holiday and there was no connection.