Thank you very much,

@Ellie ******

. Very helpful indeed.

Thank you very much for your swift reply. Cheers.

Others move after 4-6 years and others don't have the proper permission of stay or work without a work permit.

That's correct. Foreign teachers who built up a new life in Thailand are studying for a Filipine Grad. Dip. In Education. Cost about 60k and takes 1 year of study. Those courses are (still) accredited by the TCT and will lead to the teacher license.

A teacher license issued by The Teachers' Council of Thailand is required when teaching in OBEC schools (K12). If you don't have a teacher license you can apply for a temporary teaching permit aka provisional teaching permit aka waiver. Such a permit is tied to the employer you work for and is valid for 2 years. New employer means a new permit. You can get a maximum of 3 permits (latest rules). Immi and Labour want to see the license or permit when extending the visa or applying or renewing the work permit. These are the official rules.