ok, another "this is first time this happened to me" situation---  I was kind and did the "order more" thing from someone who had a popular Sue Grafton book I wanted. Well the very large envelope arrived with one end damaged and rewrapped by PO with their specially marked red and blue tape that says "Arrived damaged, USPS". I assumed a corner ripped open and they simply resealed it, but upon opening the package contained the Grafton book and nothing else.  So I marked the Grafton book rec'd on my acct, but didn't do anything about the second one as I'm optimistic that it could "magically" still reach me.   I PM'd the member to say only rec'd one book cause I thought she mailed the 2 together using DC to track cause I got a DC status msg on my acct  while it was en route.

So I don't know if because it was 2 books on 1 DC if she was given both credits when I marked one rec'd.  She offered to "gift" me back the credit for the missing book, but I told her to wait since I wasn't sure what the system does in a weird case like this!

If she used PBS DC then she got her credits, both of them, when the package was scanned. It sounds as though the package got torn open in transit (let me guess, loose in manilla envelope), one book fell out, resealed by the PO and that other book is not going to show up if they were mailed together.

If you don't mark the other book received, then you will receive your credit back when the book goes lost.

If the sender mailed both books in the same package (sometimes folks don't realize it is cheaper, and they mail them separately), then per the Help Center document "I received an empty wrapper -- no book inside" (yes, you got one book, but one is still missing, so it was half empty):

If this is a book you requested, you should not mark the book received, since you did not get the book.  You should contact the sender to let him or her know what happened.  

• The sender should call 800-ASK-USPS or go to http://postalinspectors.uspis.gov/forms/MLNtRcvd.aspx  and input the information online there. This will help USPS try to recover the book.

  • The form is titled "mail Theft"; this does not mean that you can use it only if you think the book was stolen.  "Received without contents" is an option on the page.
  • The choice to make under "Class" on the form if Media Mail was used is "Parcel Post".

Calling or filling out the mail form is likely the only hope you'll have of the book magically appearing -- otherwise, the USPS may find the book laying around, but they'll have no idea where it belongs.

She will get her credit for the 2nd book even if it goes lost-that's what the fee for the PBS DC is for-to cover lost books.  You will get your credit back when it goes lost.