The letter takes weeks

Last year, you needed to get 2 x 3 month extensions, then ask for the letter from social department.

If you don't have the letter from social department it is the same paperwork for 3 months. Luckily you have a work permit.

Your first year goes like this.

Visa from outside.

Work permit.

1st extension. 1 month, immigration interview in your office, then 2 months stamp.

2nd extension. 1 month, 2 months stamp, then apply at social department.

Get letter.

1 year extension.

Any visa or exempt entry is possible.

Possible

I did.

99.9% of the time you have to leave the country to get a volunteer visa.

A non B should be available yearly at immigration. 1900 baht plus 3800 for multiple re-entry permit.

Why can't you get it inside Thailand at immigration?

Your organization should know this. But if you can good luck to you.

I have done it 3 times personally. Always out to Vientiane to change foundations.