USPS said they delivered my package on Sunday, but it magically showed up Wednesday.
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.