I recently sent an envelope with a vehicle title to a friend in the UP. I figured since it was pretty important that I should send it certified, and to postal clerk agreed. I mailed it on a Thursday in Goshen, IN, from there I tracked it's progress and it went to South Bend, then to Ft. Wayne, sat there for 4 days, then back to South Bend, back to Ft. Wayne and back to South Bend. This took 11 days. She finally went to her local P.O. and they did something, a trace maybe, and finally on the second Friday after I mailed it, 15 days later, it arrived in Lake Linden, MI. An envelope of miscellaneous mail and paperwork I sent to her a week later arrived in three days.
Mysteries of the mail system.