I rented two books from Amazon last Sept. Amazon provided USPS return labels for the book return. I returned the books on December 21, 2013. They supposed to arrive December 29.
On Jan. 2, I received an email note from Amazon that one of the two was received. I checked USPS tracking of the two books. Both books were still shown "on transit" and the last available tracking location date is December 28. I called Amazon last week asking what I should do. I was told not to worry as the tracking information shown I did return.
Anyway, as of today, 36 days after I shipped the two books, USPS tracking still shows that the two books are "transit".