As an expat teacher in thailand it seems you can get denied sso by your employer
I read the following (https://www.ilo.org/dyn/travail/docs/1017/Social Security Act BE 2533 1990.pdf):
Section 4. This Act shall not apply to (1)3 public officials, permanent employees, daily temporary employees and hourly temporary employees of Central Administration, Provincial Administration and Local Administration but excluding monthly temporary employees; (2) Employees of foreign government or international organizations; (3) employees of employers who have offices in the country and being stationed abroad; (4) teachers or headmasters of private schools under the law on private school; (5) students, nurse students, undergraduates or interning physicians who are employees of schools, universities or hospitals; (6) other activities or employees as may be prescribed in the Royal Decree.
So if the employer says you will get SSO from us only after 5 years of working with them then you cannot apply for SSO before?