How do I know if my returned phone arrives and is accepted as trade-in?

I pre-ordered the Galaxy Note 8 on August 24th, using the MyAT&T app on my Galaxy S7 Edge.  I had paid up my S7 Edge to 50% on the Next Every Year plan, so I was able to use the app to upgrade the phone to the Note 8.  My Note 8 arrived on Sept. 6th, and I had a small glitch getting it activated, so I had to call AT&T for that, but they got it done.  On Sept. 8th I boxed up my S7 Edge after restoring it to factory, put the return label on the box and a copy of my receipt inside the box, and gave it to the post office.  According to the tracking number on the label, the return service received it on Sept. 11th.  It said there will be no further tracking as the item is no longer in the Post Office hands.  This was not an insurance claim with Asurion, so I have no way to track the phone the rest of the way.  I am wondering if I will ever know when the phone arrives wherever it's going, and if so, will I be credited for the return.  There was no instructions inside the box for this, like there is for an Asurion warranty exchange, so I'm thinking maybe I should have done this at the store.  But I know lots of people must have done this, so I'm hoping it will all work out.  I've never "Upgraded" a phone through the mail before.  

Rob