@Martin ********
No, it is not the re-entry.
For a multiple entry one year Non-OA visa, on each entry, a person is stamped in for one year (I'll call it a Non-OA visa for short).
If a person has a Non-OA visa, issued on January 1, 2021, it should be valid until December 31, 2021.
If a person enters Thailand on this visa on January 15, 2021, they would be stamped in until January 14, 2022.
If a person then leaves on September 10, 2021, and return on December 31, 2021, they would be stamped until December 30, 2022.
IF they leave on August 15, 2022, WITHOUT A RE-ENTRY PERMIT, they would need to acquire a new visa. IF the acquire a re-entry permit, they would be able to return, on the same stamp, until December 30, 2022.