I'm pretty sure they just looked at the tracking info on the carrier's website, saw it was delivered, and told you it's (probably) in their system waiting to be opened.
I really doubt they sent someone to sift through thousands of envelopes to find your tracking number on it...they also haven't physically opened many envelopes yet so UCI, receipt number, etc... are pointless.
So to everyone else who's waiting on AOR, don't waste your time with this. If it says 'delivered' it's delivered. Just hope they don't mess up and lose it in their sorting.