The last 2 shipments I have gotten the message that if I ship multiple books together I'll save postage. However, it seems that if I do that, I only get credit for one book. If I'm shipping three books, bulk or not, shouldn't I get credit for 3??

Jeri, you will get 1 credit for each book of a bulk shipment.  Well, unless you posted a box set, but I don't get the idea that's what you mean. 

I noticed for the first time yesterday that my bulk shipments (I just happened to have two of them) were each considered "1" by the Librarian when it counted how many "books" I needed to mail.  However, once I marked them mailed (and each book in a bulk shipment much be marked) they showed individually on my Books Mailed tab.  I will get credit for each one when they are marked received. 

Does that make sense?

i've only had one bulk order come in as a bulk order, but i was surprised that when i shipped it using PBS-DC, i actually got the quick credit for both books after it was scanned.  i was only expecting one credit immediately, and the other after the book was received so it was a nice surprise.