As has been stated earlier, this is USPS. I had a similar issue where I ordered something from overseas and they sent it express but neglected to tell me. In the meantime, I got busy with work and wasn't worried about an overseas package taking its time to get here. Package slips are usually left in my mail box but I never see one ... until a month later when I open the little-used front door to find one stuck between the front door and the storm door (not visible when the storm door is closed, of course). I head over the post office to pick it up and find it was returned to the sender because it was "express".

I can't count the number of times I've gotten the "you weren't home" slips in the mailbox ... even when I was home all day. It almost makes you want to laugh when watching TV shows or movies from the 50s or 60s when USPS lived up to their motto.