Why not email and ask? There is a contact email on the Thailand Pass site. I would think you could upload your documents including one indicated "old passport", one "current passport" perhaps...or you could try with just using new passport info and see if it's approved.
I read this as if you were a resident of Thailand for marriage, work, education ...actually became a resident. Assuming you were in Thailand for 6 months for tourism purposes? that does not mean you were a resident of Thailand.