It is still on the delivery window, i know it sounds ridiculous but some people waited for 60 days to receive theirs back. Mine took a little over a month to show up. The passport agency actually held my certificate for 30 days even before they mailed it back to me. If it gets lost the passport agency will not cover the loss (it is stated on their website), USPS will not cover it either, you will be on your own for the reissue fee with USCIS. Unless you really need the certificate for special clearance for a federal job a passport is all you really need. even if you petition somebody you don't need the original as long as you made a copy before you mailed it out for the passport.