Sorry Danny I removed my comment. The pictures I mentioned are actually for the non-B renewal and not the actual work permit. Got a bit mixed up. Nice to hear it's a fun company you work for :)
I live on the BKK/Nonthaburi border but on the Nonthaburi side. My work is in BKK so visa is processed through Chaengwattana. I'd assume Nonthaburi Immigration would be correct for you. The only time I have to go to Nonthaburi is for my 90 day report.
I wish I had known it before that day. I went early to get it done quickly and then had to go back home and by the time I got back there was a queue and ended up waiting 3 hours. Nonthaburi Immigration :/ Small and crowded. I've been in and out 3 times since and I've always remembered to bring it. Lesson learned I guess.
I guess they see you as arriving at the airport as they know you are here or whatever so it restarts another 90 days to let them know you are still here :/
I've always gone 90 days from when I arrived back in Thailand. The only thing I had to bring extra was a TM30. It's basically notifying your address again. I didn't bring it originally and the immigration officer said he couldn't accept my 90 day report without it.
I was in a similar situation with the Bank. I tried SCB and they said they had to call HO and would get back to me. Went down the street to KBank and 20 minutes later I had a new bank account :D All they wanted was my passport.
One guy was asking for advice about it last week as he was denied entry. A quick look at his profile showed that he was working as a model/actor on a tourist visa. Posts like "I'm working while I'm on holiday". Then he wondered why he was denied...
I don't think you can convert it but I was originally on a Non-O and applied for a Non-B at renewal time and was granted it. All done at Chaengwattana.