Hello, i don't think you can claim a key if it was bought in a bundle.
From what i understand some games in some bundles don't give keys(and others do?). I have no idea what controls this but it was likely done to prevent people who are trying to resell keys from flooding the market with lots of them bought for cheap in big bundles. Judging by the number of keys left - people who bought the game normally were able to claim them, but people who got it from a bundle - didn't. (bundle brought 10x the amount of downloads it had before and the number of used up keys is close to what it was).
Didn't know this myself until just now. Hope this clears things up.