I called FedEx support and they explained me why this happens. Turns out, people who deliver packages/mail have strict deadline to deliver their packages and on days when there are just too many for them to finish delivering everything, they mark it as delivered and actually deliver the package on the day after.
Sorting this out the first time was me spending hours on the phone calling between DHL and USPS to find out where the package was and what was happening.
Even more inane is that USPS uses a ~20 digit number for tracking packages. Imagine reading that on the phone to a customer support person. I can't believe nobody thought to use base-32 encoding [0].
[0] https://github.com/stickfigure/unsuck/blob/b4dff541d756303ca...
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.
This is all speculation based on my experiences with USPS.
It defeats the whole purpose of tracking.
If employees are doing this, this means something else should change, either extend delivery times, hire more people, optimize how things are done etc
I honestly believe many delivery drivers (not just USPS, but Amazon, UPS, FedEx, etc) are brazen because they get away with it 99% of the time.
At my house we have a communal mailbox bank (which seems to be normal now for most new construction). I would bet that 1/4 packages of mine are delivered to the wrong box / placed in the wrong box. So some of it now can at least be attributed to those mistakes.
It is possible that this is what is happening, but I don't think it is likely.
It's all down to your individual carriers and local depot management though. My local Fedex Ground depot doesn't seem to care at all, so my only recourse is to avoid having things I care about shipped Fedex. Which by itself is another reason the USPS needs to be kept operating - so at least we have three options instead of the characteristic duopoly of modern antitrust enforcement.
- they don't get scanned into tracking until they get processed at the facility, which can take a day
- they sometimes get scanned "out" when they're loaded onto the truck, rather than at delivery point.
Since the directive is now to leave on time, rather than wait for all the packages to make it onto the truck, I bet they're getting scanned out and then waiting on the floor for the next day's truck to actually get delivered.
UPS/FedEx etc use handheld scanners at the delivery point, so they have to deal with employees faking delivery and making up for it later.