@Dar***
, I guess he needs to talk with his agent/accountant more deeply about details of the process and schedule.
I'm not expert and I cannot say for sure, though some government papers which necessary for Non-B application have validity or expiration date (don't know the right words), 1 - 3 months.
As you mentioned, if he is going to Penang for Non-B single, he already has wp3, that means also his WP might be already applied.
And if he out of Thailand more than 90 days, when he wants to apply Non-B multi after that, his WP may or may NOT have 8 months left which required as
@Ma***
said.
I'm sorry this is just a possibility that I could imagine so full of "might/may" and I apologize if this is off topic.