Actually I would call Apple ASAP and give them a heads-up about this, fedex did the same with mine and it completely screwed everything up.
Big Karen-y rant ahead...
First off the trade in box was late after it showed out for delivery for 2 days, but I packed up my 8+ and dropped it off at the fedex store the same day. It has now been stuck at a fedex center in PA since Monday due to an issue with the address after the employee at the fedex store 'corrected' the address on the prepaid shipping label instead of just scanning it and putting it in the outgoing bin like she was supposed to. Now the package is undeliverable.
I've called fedex twice and gotten different stories each time, first they said it's going to be sent back to me since the destination address is now wrong and I just need to give the tracking 24hrs to update. I waited 24hrs and it didn't update, so I called them back. This time they said *I* placed a restriction on the package(which I definitely did NOT, idk what they're talking about) but they couldn't see what the restriction was so they'd have to transfer me to the shipping center to sort it out. They put me on hold for several mins then came back and told me the shipping center won't talk to me and I'd have to have Apple contact them. I'm beyond pissed at this point. So I call Apple and the rep said this is absurd and 100% fedex's fault. She said I would still get my trade-in credit, it would just take a bit longer since they'd have to investigate but the trade in team has seen this many times before and they'll get it taken care of.
I'm never mailing in a trade EVER again, in-store trades only from now on. If it does get sent back to me, I'm canceling the trade and just selling it or keeping it as a backup phone. Fedex sucks, I've never had a problem like this with UPS.