I had USPS report a package "delivered" but it never showed up. Waited a few days, contacted the vendor who shipped out a replacement (it was a couple of bucks of mechanical bits).

Two months later I open up the mailbox and there's the original shipment.

I have to wonder if they actually track anything. It feels more like they make an estimate of the delivery route/time and play it back to you regardless of whether it's actually happening.