I requested a book that was later declared lost in the mail. That book was then automatically added to my WL.  Another member later posted that book. As I had not yet received the first one, I accepted the book.  Today one of those 2 books arrived in the mail. The return adress is that of PBS, so I have no idea who sent it. Who should I give the credit to? The 1st sender or the 2nd one? It is possible that the copy I received today could be the 1st one but I'm not sure. Any suggestions or advice? 

Does it have a post mark on it?  If it does was it mailed before the second sender sent it out? 

Mystery solved. I went to usps.gov and found the state the book was mailed from. Fortunately, they were mailed from different states!

If they used a PBS wrapper there should be a transaction number on it.  You can compare with your transaction archive to see who sent it.

If they used a PBS wrapper there should be a transaction number  - Just an FYI - that request ID# on the package does not show anywhere on our TA or requests. If you are unable to identify a transaction, you can send that number to TPBST and they can look it up, but it is pretty much useless to us as members because the package is the only place we can see it.

A DC number is traceable, which it sounds like maybe thats what Jason used through USPS, but you could also compare a DC number to the ones on the transaction on PBS to identify which transaction it went to.

You're right.  Why was I so convinced we could cross check?

'Cause that would seem logical? It would less work for them if we could look it up ourselves.

Out of my unnecessary curiosity, was it the second book or the first one?