im not sure why this is happening, but the number of books i have mailed keeps going down. 

is it b/c when the person receives the book and gives me a credit, that book is "deducted" from number of books mailed, or what? 

the other day it was 21 (i just joined) and now its 19.....im just confused.

Do you mean on your Member center? Then, yes, once a book is mailed and received, then you get the credit and it is removed from your Member Center.  However, if you look on your transaction archive, you'll see the details.

Yes, as soon as they  mark it received, you get your credit and it disappears from the books mailed tab.  So your number of credits will be higher as books disappear from your tab.

ok, thats what i thought. just couldnt figure out why "number of books mailed" would ever decrease....counterintuitive yk?

thanks all!

Yes, the wording does make it kind of conterintuitive. 

Your Public Profile and your Transaction Archive gives the all time total of books mailed.  I'm confused about where you are looking.

In the main page tab the Books I have Mailed are only the active ones. This is so you can see what hasn't been marked received and keep an eye on one that might be close to going "lost".  It'll give a seperate account of all your transactions in a different spot.