That is indeed what Immigration has posted on their website, and yet the Cabinet decision and subsequent Royal Gazette announcement don't say that at all - they just say that 90 day reporting isn't required thru September 26, which is why people like the OP are confused. Given the conflict, I agree with you that the safest course is to follow the earlier date, even if it's not clear how they came up with it!
The same thing happened recently to friends of mine, and the issue really was about the Thai wife's registered address, not the American husband's. The husband wanted an extension because the wife was being treated for cancer, and the IO accepted that they were married and that they lived in their own condo in Bangkok, but she said that the extension could not be processed at CW because the address on the wife's Thai ID card was still her mother's address in Nonthaburi. To get the 60 day extension, the officer said they would either have to apply in Nonthaburi or else change the address on the ID card to Bangkok and come back to CW. She didn't care at all about the address on the TM-30.
I went with an appointment last week, and they did indeed see me at the appointed time (after I grabbed an assistant passing by to show her my appointment slip). I still had to wait 40 minutes for the final sign-off by the supervisor, though, just like in the past. The reentry permit took only seven minutes start to finish, however, with no appointment.