Just went to labour in Dindaeng to have my WP processed. I am not sure if this is a new rule but they said it is. So once you have NON-B, you have to process your WP not more than a month or else your WP expires same as your NON- B visa (90 days) then it needs to be renewed.
So in my case, I got my NON-B on June 13 and expires on Sept. 10 (90 days as usual) this year and my contract ends on April 31 next year. Just processed my WP yesterday and they said my WP will expire on Sept. 10 and my WP needs to be renewed once done with my visa extension in Chaengwattana. Usually, staff from Labour will base whatever is written in your contract. If your contract ends next year then your wp expires next year.
Now, I have to pay twice at Labour. 750 baht until September 10 and another 3,000 baht until April 31.