Yes, it's really hard to check someone else's DLC.

I was more saying that anyone can always enter for any package giveaway, and that the person entering the GA needs to check their own library before entering if they're not already sure if they own things or not.

BTW, if the user sets up ESGST and configures it correctly, they'll get a count of the number of items they own in a package. And, of course, if that count is the same as the number of items in the package, then they'll know that they already own everything even without having to go and manually check their library.