Gold has an earlier check in time and thus has the opportunity to book an earlier PAT. If you don't book an earlier time, your boarding number is higher. There's no automatic assignment of boarding time based on your CC status. I've heard recently that you aren't required to book a PAT when taking
DCL transfers from MCO. We've always been required to pick a PAT even when taking transfers although we've always been coming from WDW resorts and get to Port Canaveral after open boarding. If you're taking the bus from MCO and not required to pick a PAT, I suspect it has to do with the time/order you're boarding the bus and what PATs are left. I would presume that they assign them in the background even if you don't see them and it's basically first-come-first-served. To me it would make sense. If everyone else has already picked most of the early PATs and you're not required to choose one when taking the DCL transfers from MCO, letting everyone on board the bus get on the ship early would totally negate the purpose of using PATs and boarding numbers to smoothly and evenly board everyone.