Technically, in order to follow the site's rules, you should still mark it as Not Received and have me delete the giveaway, regardless of the eventual disposition of the key (marking it as Received indicates you have redeemed that key specifically to the Steam account associated with your SteamGifts account, and that it wasn't a duplicate).

The only thing I can think of to avoid is using the key in your own giveaway here (re-gifting), but it's perfectly fine to donate it outside of the giveaway system (even if still on this site) with my full approval.. Having said that, as DLC I don't think there's any real way to detect a (minor) violation of the rules here (even if you use SGTools), so if you're not as anally retentive (well, slightly nit-pickingly autistic) as I am then feel free not to jump through these hoops. ;-)

In any case, I'm happier for you disposing of the key as you wish than me having to do it. :-)

P.S. No worries. I sometimes get do-gooders advising me to restrict my giveaways beyond level 0 or I'm asking for trouble or letting bots snatch keys, but I rarely get any trouble from my bundle spares, and I like to be as inclusive as possible, these people can't possibly understand the circumstances of folks in all parts of the world, and I occasionally get a pleasant "OMG I won, thanks so much!" comment as a result.