<p>Actually I was mistaken when I referred to registered mail as I used certified last year.</p>
<p>You state that registered is only one day slower than certified, but certified mail is (or at least can be) also slower than standard priority mail. USPS states “Certified Mail items travel at the speed of the mail class with which they are purchased” but when our IDOC package (priority, certified) failed to show up as delivered for over two weeks last year, USPS told us that sending things certified “can” slow the package down. (Sending it registered would have made it more trackable, at least.) We finally re-sent the package, and then they both showed up within a day of one another.</p>