Received a book today from Tennessee. The label is just one of the PBS printed labels where you add your own postage, it is NOT a paid label. There are no stamps or postmarks anywhere on the package. On the bottom left corner, there is a sticker that was added with my zip code and a barcode, but I have never seen one of those stickers and no postage. I've seen a variety of types of printed postage from the PO, but none of them are on the package, just the little square barcode. 

Weird? 

sometime the stamps could have fall off also sometime in rare case the USPS fails to notice there are no stamps

on the package -rare but it had happen

My guess is someone saw the nice professional printed PBS label and just assumed it was prepaid? Maybe the sender forgot stamps (it was light enough to drop in a box) or maybe someone at the counter got confused or maybe someone at the sorting center got confused. 

Weird! 

At least it didn't arrive postage due. 

Like Mark commented Becca, I've seen it go both ways.  Sometimes a nicely printed label slips by without any postage, and once in a while postage falls off enroute.  I've seen members upset because they received a book postage due, yet the sender has proof of paying postage (fell off enroute) and therefore the postage was paid twice.

The little square printed barcode sounds like the latest intelligent postage and the barcode should carry all the information such as date,input location, destination location, postage paid, package weight, as well as provide various large mailers tracking info.  Some of the various newer sorting machines will read all that and be looking for fraud info (i.e. reused postage, weights that mismatch what was paid for, etc).

It was just a regular bar code, not one of the fancy pixelated ones, if that is what you are referring to. I've never seen one before without postage.

I just got a DVD on SwapADVD that arrived without any postage at all. Also in the pre-printed wrapper with a DC barcode, even. Nice to meet someone else sharing my moment of O_o??

A year or so ago, my husband offered to start mailing my PBS packages for me since he knew I hated standing in line in the post office and he had to go to the post office for work a lot.  I left him two packages with DC barcodes (but not printable postage) on them.  He mistook the logo where the stamps go as postage (since he knew I had used printable postage in the past) and dropped them into the mailbox just like that.  I got a nasty PM from the member who received the first book, and after I refunded her credit and apologized (I bit my tongue about how she shouldn't have accused me to of trying to cheat her out of a credit!), I then PMed the other member and explained what happened, and told them that if the book arrived postage due, they could refuse it (so it would come back to me postage due) or pay it, and I'd buddy them a credit, but I hoped it would arrive without incident.  Never heard back from them, except that they eventually marked the book received. 

I have also received a couple of books through PBS with no postage on them.  One looked like the stamps had fallen off, but the other looked like there had never been any postage.  I PMed the second member and explained what happened just as a heads up to them. 

I've also received several books that clearly didn't have enough postage on them, but the only one that arrived postage due was where the member's husband mailed the book for her and forgot to write "Media Mail" on the handwritten label, so the postage due was for the difference between media mail and first class postage. 

I just got one from TX today.  It had DC, but absolutely no postage on it.  It didn't arrive "postage due" either... I'm amazed that it arrived!