I really doubt UPS does. But I do think 2 things happen, one has already been mentioned about how UPS delivers the package to USPS (so as far as their tracking

I really doubt UPS does. But I do think 2 things happen, one has already been mentioned about how UPS delivers the package to USPS (so as far as their tracking is concerned its delivered), then it takes USPS another day. The other one is when Amazon uses laser (lazer) ship. I cannot stand that company. They are horribly late, constantly mark packages as delivered when they aren't and their drivers (at least in our area) treat our packages poorly. We have called Amazon and filed a number of complaints about Lazer ship and honestly in the past 4 months or so we haven't had anymore packages shipped via lazer ship. I don't know if our complaining helped or what but man am I glad. We love our Amazon Prime and order a ton of stuff using it, but it was starting to become a problem.