However, I have shipped thousands of Priority packages, and that delivery confirmation shit is not as reliable as I would like. Sometimes stuff gets accidentally scanned prematurely and shows up as "delivered" 2-3 days before the person receives their package. It's not corrected by whomever screws up, I guess they figure if you really cared you'd have used UPS. So every month or two I get frantic people telling me "you must have sent it to the wrong address!!@# It shows delivered but it's definitely not here!" They usually get it within the next few days.
On the upside for USPS, I've never lost a package inside the US, which is pretty impressive. On the rare occasions people think their package was lost in transit it's almost always their fault - someone else checked the mail and stuck it in a corner, and they come back a week later and apologize.
Best of luck either way.
Yep USPS lied about when it was delivered