I too have the issue of no trade in credit. Something is wrong with Verizon's system. I used the box and the label Verizon provided for each of 3 phones. No credit has been received. For the one label that I printed out and put in my own box, the phone was successfully credited.
It can't be coincidence that all these people can't get their trade in credits. All I have is copies of the email with the submission ID. I don't have tracking numbers - why would I take a picture of a label that Verizon sent me?
I am at wits end - and am ready to leave Verizon - I am tired of paying you money when you can't find the credit for 3 of my trade ins.