Today I learned USPS recycles tracking numbers.
https://sellercentral.amazon.com/seller-forums/discussions/t/3b628bfe-6cc7-40ec-894a-13f196be2402
I bought something off eBay back in December. The seller printed a shipping label, but never shipped it. A couple weeks later I opened a case with eBay and was promptly refunded.
But.
The tracking number is still out there, and now used again. Last night I got an email from eBay "Your item is now with the carrier". The new package was shipped in PA, my order was coming from WI. Hopefully eBay doesn't screw this up too bad and try to re-charge me for the original package.