i mailed a book [picked by the mailman] on may 20th

see  below but  its already  the 23rd [tomorrow is the 24th 

yes it hasn't been scanned why  does  it take so long? what are they

waiting for - CHRITMAs ?  i dont get instant credit  so i have wait until the PO scan

my package

DC=DELIVERY confirmation

Most packages with DC will be scanned several times along the way to the destination, but it is not guaranteed.  The package may not receive any scans until it is delivered.

The first entry that you should see is:

Electronic Shipping Info Received

From what I understand, that is required for USPS to know that it should send the scan information to PBS. Since you are not seeing that first entry, USPS may be scanning your book, but it does not know to send the information to PBS. From what I've seen, there is sometimes a delay in the communications between PBS and USPS. Once the communication goes though, you may see several scans appear at once that have happened over the previous days while the book was in transit.

this what get from usps 

USPS Tracking™

 

Customer Service ›

Have questions? We're here to help.

 

Hi Mark!  I sent you a PM regarding tracking for your number.

Previously known as Delivery Confirmation, USPS Tracking is just that...delivery confirmation.  For the past several years USPS has been minimizing the handling of packages enroute...and thus fewer actual scans.  Sometimes they will pick up an 'automated' enroute scan, but more and more frequently we are only seeing the actual 'Delivered' scan.

Couple weeks ago I mailed 4 books at the PO.  Mailing from the counter, all 4 should have been scanned as 'Accepted' and transferred my PBS credits within 24 hours.  Only 3 of the packages picked up the "Acceptance" scan and after all 3 of those were delivered, the 4th package finally picked up it's first USPS scan..."Arrival at Unit" 

And packages mailed from locations other than over-the-counter pick up fewer scans.  IIRC those packages not hand scanned at the counter are processed in bulk on a conveyer belt and the automated scanners can be hit or miss, depending on the orientation of the barcode when it passes over the conveyer.  Don't worry tho, your package will probably arrive just fine in a few days.