How do work permit and visa expiry dates differ in Thailand, and is the visa still valid if I cancel my work permit?

The retirement visa and work permit are two separate documents with different governing authorities and purposes. The work permit, issued by the Ministry of Labor, allows you to work in Thailand, while the extension of stay comes from the Royal Thai Police Immigration Bureau and permits your residence in the country. The different expiry dates reflect their separate purposes and regulations. If you cancel your work permit, your visa will still remain valid until its own expiry date.