I mailed a couple books on 7/3 yet it still says accepted at the p.o. under details- why isn't it showing anything else- is it still there?  I am concerned the requester won't get them..

It's not still there - it just hasn't been scanned anywhere else.  Probably on a truck somewhere, on its way.

doesn't it usually say enroute?

usually if the package doens't have any other scans after the acceptance scan, it's because the bar code is messed up and can't be scanned. If the ink is running out or if it "flakes off" when other packages rub up against it, that can make it unscannable. If you tape all the way over the bar code and the tape is wrinkled or if it's cloudy, it can also be unscannable. 

Most scans along the way are automated, the package is on a conveyor belt and goes under a scanner, if the scanner cant read it, it just passes though like a package without a barcode.

Sometimes the books get scanned but there is an issue with having them appear. Every once in a while I will mail a book and wonder about it. Then all of a sudden scans from the past show up all at once. I think the issue is with having the scan transmitted to PBS.