After the first year, I believe you step out of the country just before its due to expire, return to Thailand and they stamp you in for another year..I think that's how it works.
So the theory goes. I have METV and have been in Thailand since August 1st. Extended by one month then did obligatory bounce. Coming back into HKT I was taken aside and grilled. My final day for entry this METV is January 24th. I was told by the I/O big cheese that they may not let me back in on the 23rd January which is when when I was planning on returning from home, to use up my allowance, so to speak. Plenty of coin, no issues, good clean living character, I really do not understand the hoo-haa.🤔