I'm not sure if this is relevant to your situation or not, but I'll share I know about the USPS or at least my local office. I use USPS on a regular basis for cheaper items, like $300 or less, however I don't like to use them for more expensive cues and ebay items because of what I see is a flaw in their system.
I use USPS 'Click N Ship' I think is what it's called, where I basically created an account with the USPS website and I go in and create my own shipping labels, pay for them, print them, etc... all online. So basically all I have to do is drop off the package at the USPS or let my mailman pick it up.
The flaw is: When I use Click N Ship or create a label through the PayPal system, my local USPS office will REFUSE to give me a receipt when I drop the package off. They say the receipt 'service' is only if you pay for the postage at the actual counter of the post office (which means paying full price as Click N Ship has a slightly cheaper rate). To me, this is crazy.... I have to literally hand them a package and then just cross my fingers and hope they don't lose it before it's scanned. Otherwise there is no 'proof' that I actually gave them the package.
Now, I don't know if this is just my local post offices being an arse or what, but I do know that I've had several post offices in my area tell me the same thing. I even called the USPS 1-800 number or whatever it is and was told the same thing as well.
That's why now, anytime I have a package over $300 or so, I will send it FedEx as they WILL give me a drop off receipt without question, even if the label is prepaid from an online account.
Anyway...I say all this because I guess there is a chance this cue shipper printed his own label and did drop off the cue, however has no 'drop off receipt'. I remember once I had my mailman pick up TWO cues on the same day going to different locations, one cue was scanned that evening at a local sort office and then had scans all the way to destination. The other cue literally had NO scans until the 'delivered' scan. *sigh*
I'll close by saying one trick I have started using that may or may not help. After I create a label online, I will immediately go in and schedule a package pickup online for my address the next day. Then when the package is picked up, I get a confirmation email showing 'a' package pickup was completed as requested. Now...the pickup is not linked to the tracking number of the package that was actually picked up, but my thoughts are that at least I have a little proof that a pickup was made
Anyway...good luck to the OP on getting your cue, hopefully it'll come through for you.