The initial extension is based on the visa, in no way is it an extension of it. Subsequent extension could well be for a different reason than your initial visa was issued.
It is 🙂 To be fair, that pension is paid directly into my Thai account, and I have to provide them with my yearly pension statement and all my Thai bank statements. I should have made that clearer in my post.
Nope, the reason they stopped issuing letters was because Thai immigration wanted the embassies to verify/confirm the income, which they obviously could not do.