Unredeemed Promo Codes: do they return to my iTunes Connect Account?

Thanks for your response vinnyvg. I have benefited from the guidance you've given to others and appreciate your contributions.

On the Promo Code issue, I apologize for not asking the question in a fuller context. I became familiar with the process on the first MutiTouch Book I published in Nov 2012. I distributed all 50 codes on my recent MultiTouch Book published in March. Before I asked the question in this forum, I checked the Promo Code status of my first title and found that there were 25 codes still remaining. I could have sworn I sent out all 50 (it's surprising how many candidates you find in a position of influence). But when I checked the stats my recent title with iTunes Connect by "Type of Transaction", I saw that there were not 50 free downloads; a number of codes were not redeemed and had just expired before use. Yet these unredeemed Promo Codes have not returned to my account.

It is perfectly understandable to set a limit on these free download codes. After all, Apple can't have every author sending out hundreds of free codes because if they did alllow authors to do this, oh, we would (online marketing opportunies never end). While there is some nominal cost, however small, every time their server is hit, costs could prove significant in large numbers. However, the only value to the Promo codes is if they are actually used. Apple has a 30% interest in this issue. It seems counterproductive - and unfair - to simply let the codes vanish.

Follow up: To be clear, when I wrote "the only value to the Promo codes is if they are used" I was referring to the codes being REDEEMED.