Humbundle Question: Gifting Old Keys?

I was just looking through old Humble Bundles I'd bought with the intention of creating a giveaway for a key I hadn't yet used. I noticed that for bundles sold before the gifting/redemption rules changed, there is no little present button next to the key generator, however the description in the box says 'Click the button to redeem on Steam'. (Pic) I don't want to click the button in case I accidentally redeem the key on my Steam account (I already own the game I wanted to give away, so the key would be wasted). If there's no button to gift the key and I can no longer generate a key, does this mean I can't give away the key at all?

Sorry if this has been answered before, but the Humble support page didn't say anything about it and I couldn't find anything about it here.