Hey there! If you have a different version then just add your own! You can list the main difference on the game title itself (enclosed in parenthesis) and then use the description box to explain what's so different about it.
For example, a game that was included in a magazine could be added as "Game title (Fullgames release)", then in the release date you add the month the magazine was released. I'm not sure what to use as the cover, though. The front of the magazine, or the CD itself? I'd go with the front of the magazine, myself! And since we don't have a PC-Brazil region... then I guess we should have one now!
The covers seem to be available at Fullgames' website, so you can use those if you wish.
As for missing games such as Assassin's Creed II, well, when the database was created, it didn't account for many newer games. So if it's not here, then just add it with the proper scans and other data if possible.
If you have any other questions, feel free to ask!
(P.S. - to the other admins, these magazine releases are completely legit releases. I have a few from a now-closed magazine from Spain, and I got a free Steam game thanks to a giveaway by a Brazilian magazine.)