I have had that happen with books I requested and all was well. The PO does not seem to be scanning DC mail as much as they used to and consequently I have received books that were never once scanned! If indeed the books are declared "Lost" your credits will be returned to you, so worry not!

If they books are not recieved within 26 days they should still go lost in the mail like normal, which means you should get your credits back then.  This is what I could find on the subject in the Help Center:

If your book is declared lost in the Mail at PBS or is returned to you by USPS for some reason, you get to keep the Instant Credit.

Obviously that's more on the senders side, but it inidcates to me that they can go lost like a normal PBS book. 

If a book is not marked received, and therefore goes lost, the requestor ALWAYS gets their credit(s) back, regardless of anything else.

Normally, the sender of the book would not get a credit, because the book has not been marked received. (So, they have presumably lost the book they mailed AND the credit that they would have received for it). However, if the sender of the book used PBS postage, OR used PBS DC (and the book has been scanned at least once while en route), then they also keep the credit that they have received for the book from PBS (which is part of the fee that they have paid to use either service). The PBS Credit Guarantees are guarantees to the SENDER of the book that they will receive the credit for the book, regardless of what the Post Office does with the book. The PBS credit guarantees have nothing to do with the book receiver.

I recently mailed out 2 separte orders, both using PBS postage.  One has been received and the other only says 'Electronic Shipping Info Received'.  It is possilbe to have that message even though the person did mail the book. 

I mailed a book that had DC and it wasn't scanned at the our post office.  In fact, it wasn't scanned until it was almost at the receiver's house!  (Annoyed the heck out of me).

Don't worry about it yet.  The Post Office seems to be inconsistent (smile).

Yes, I think they are scanning books less of late. I always drop my books in the blue box in front of my work. I use the PBS postage and typically they would have a scan recorded during the night after I mailed them in our local distribution center in Minneapolis. However, recently that scan is missing about half the time, so it often goes several days before it says anything but "Electronic Shipping Info Received." It's weird because sometimes I'll mail half a dozen books at once in the same box, and several will be scanned and several not. Who knows what they are up to!

As others said, though, no need to worry...your credits will be returned if the books do end up "lost" and if they were wishlisted books you will be put back on the list at the front of the line.

Cheryl

I just had this happen to me.  DC was purchased, but the book was never scanned or delivered.  It went lost on Saturday and my credit was returned.  Still hoping that the book was indeed mailed and that it will show up, but I have a feeling I'm just going to have to wait for the next book to be posted.