On Friday I recieved a book in the mail . I went to my computer to mark it rec. and marked another b ook by the same author  rec'd. This book was mailed with dc on april 25th.  the other much later.  I pm the sender to tell of the mistake and  I have not gotten a response yet.  I still have not rec'd the book.  Today  I looked up the tracking ,usps said notified book was to be sent 4/25 but nothing in the system as yet. Should I pm the sender again or just wait it out and eat the credit if it does not come.  MY  mistake.

I would wait. The book could easily be in the mail and not get scanned until it gets delivered to you. If you do not get the book, it is a lessoned learned on not marking books as received until you have them because there is no undoing that step.

There's nothing the sender can do for you.  They can't unmark it as received or make the mail go faster.

Here's some info from the Help Center:

Once you mark a book as received there is no way to undo this action.  The software simply doesn't "go backward" in that way.  

• When you did this, the sender got credit for sending the book.
• You can contact the sender to discuss this if you want.  To do this:
  • Go to your Transaction Archive page under My Account in the toolbar at the top of the site
  • Scroll down to see the completed transaction for this book on the Transaction Archive page
  • Click to send a message to this sender
    • If the sender does not respond within a week, please let us know

If you marked a book received with a problem and there was not a problem with the book, you can change the swap status as described in Follow-up on Problem swaps.  Doing this will not "un-mark" the book received, but it will remove the "problem" mark from the completed transaction.

If you marked a book received accidentally from the En Route to Me tab in My Account:

• This book was marked mailed; chances are that it will arrive.
• Please wait for your book; most likely it will arrive and you will have already marked it as received, and won't have to do anything further.
• Please try to be very careful about which books you mark received.

Thank you for the help.  I'm sure it will come. fairly new and love this site. becoming an addiction.