Happy face, I don't know much as you seem to think, but from what I know, if you have already got the EAD card, you can use it. However, your application will be pending until your priority date is current. USCIS will not accept any new application, but if they have accepted it and is pending, you'll have to wait for your priority date. You might get lucky and get processed earlier too. You never know with the USCIS.