How can I extend my single-entry TR visa in Chiang Mai without an embassy letter?

Successfully extended until 30.11 WITHOUT embassy letter.

Chiang Mai, Promenada mall. Last month I got the REGULAR 30-day extension of my single-entry TR visa, stamped until 26.10 (so I didn't use any embassy letter, also because my embassy wasn't release any).

Last week I went to the immigration office to get the extension, but they turned me away because of no embassy letter.

I gave it a try again today after reading some posts in here saying that at some IO embassy letters were no longer needed and I successfully got stamped until 30.11

Didn't have to pay anything.

Again it seems like a hit-or-miss sort of thing. And apparently CM is a lucky one.