Fwiw on several occasions I've had packages delivered to the wrong address (e.g. 200 East Main not 200 West Main) that were obviously "redelivered" by whoever lives at that address. This could explain your findings perhaps?
I live in a rural area (this time of year I can only see one other house from my house), and I have had a few delivery people complain that they couldn't find my house when looking for it on East Joy Rd instead of West Joy, but the fact that my address doesn't exist on the other side helps. I also know most of my neighbors and I am pretty sure none of them are walking the packages over.
It is possible that this is what is happening, but I don't think it is likely.
Personally I experience this way more with Fedex - literally its nearly every time. I haven't had this happen except for a couple of times with USPS over the last 2-3 years (been in the same apartment for about that long).
I have the same experience, with one or two USPS fake deliveries. None from UPS that I can recall (but fewer packages overall than USPS). Meanwhile Fedex Ground has seemingly adopted a policy of doing whatever it takes to mark a package as delivered, including just leaving them down by the road where they can be easily stolen.
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.
I had that happen with UPS at my last address: One of my relatives put the wrong address on a box, and then UPS decided to deliver the next 5 boxes to that same wrong address. At least it was consistent and I knew where to look.