It was stated in another thread that requestor AND sender get their credit back when a book goes lost....If this is so then why does anyone need PBS DC?
I checked Help Center and could find nothing about the sender receiving a refund.

I've never had a book go lost in the mail but if I remember correctly I think it's just the requester that gets their credit back. I think the sender is pretty much out of luck unless they used the PBS DC.

The sender does not get a credit if a book is lost in the mail unless they used the PBS DC.

From the help center:

A book I sent is lost in the mail!

If your book does not arrive by the 26th day after you marked it mailed, it will be declared Lost in the Mail at PBS.  This does not mean that the book is actually lost; it may simply be delayed en route.  Also, the requestor may be away from home and unaware if the book has arrived.  If so, he or she can mark it received from his or her Transaction Archive when he or she returns home, and credit will be granted when she or he does that.

A book sent to an active member at PBS will not earn credit until the requestor marks it received, unless PBS Delivery Confirmation is used to send the book. 

I believe prior to pbs dc both people got their credit back. Now it is just the requester. One more reason to use pbs dc. I use it for everything, even on non-pbs packages!