GTA IV's was/is extra broken because there's GTA IV, GTA IV: Episodes from Liberty City and GTA IV: Complete. And they'd always put the latter on sale, but not the Episodes, yet if you had the first one you couldn't purchase the Complete Edition. Eventually someone must have noticed/notified 2K because they put Episodes on sale.
Now, this was just in Steam. Then you had to deal with GFWL to register the Episodes or some bullshit that had the same problem where you "owned" something discontinued but the system thinks you already had "Complete." (Plus Rockstar Social Club!)