Q: Are you allowed to enter packs if you already own a game?

I would enter, then if you do win ask the gifter if they are OK with it. If they are not tell them to re-roll it.

Owning one game in a pack of two vs. one game in a pack of 24 are pretty different. I think most people would be okay with the latter more so the former.

Same thing bothered me as well. But since SG allow you to enter it should be quite allright to try to win (in case you did the sync recently). There is some limit, like if you own 2/3 games from the pack you cannot enter. Or pretty close to it. So what SG allow me to enter, that I will. I guess...

You can, but think about entering giveaway if you own like 10/24 games from it.

Doesnt portal kind of stack in your inventory if you buy a pack with portal in it? Which makes this a moot point because even if the gifter was for some reasons upset, you could just send them back portal to reroll. An offical stance on packs and DLC GOTYS should be given for the community. Its rather arbitrary to leave it as "well let the gifter decide if they are mad". Not to mention unfair to the winner and community. The winner gets a win notch without actually getting anything, and the gifter gets another notch for a gift given/received.

Kind of annoying to avoid entering packs and bundles because I may own the base game w/o the dlc or because I may own one or two of the games.

I just ask the giveaway maker their views on it. Some will be okay with it, others won't be.

If it's a big pack, like the valve pack in the example, and you only own 1-2 games for it I'd be fine with you entering, most other cases, not so much. It's kinda like people entering for Complete packages when they already own the base game. What you already own will magically disappear when you activate it so I'd much rather it go to someone that will enjoy the full thing.

We always leave that decision up to the submitter of the giveaway. There isn't a general policy against it, however.