The Delivery Confirmation No (which you HAVE to purchase if you ship using paypal - free for Priority shipping though), is just that, a confirmation of delivery, not a tracking number, although a lot of my customers seem to think it does both!
Just a heads up for future transactions - if you don't provide Delivery Confirmation, and the buyer files an 'item not received' dispute with paypal, you will automatically lose. To have seller protection from paypal you have to ship to a confirmed address, with D.C.
Doesn't help here of course - I would just let them know the date you sent the item, and the no of days quoted for delivery (2/3 priority mail), and ask them to contact you if it hasn't arrived within a week or so.