GOG is doing this a lot.
I have the soundtrack, soundtrack is not marked as owned.
I have everything in Deluxe Edition, Deluxe Edition is not marked as owned
Darksiders - I have everything in Blades & Whip Franchise Pack, not marked as owned.
Dishonored - I have everything in Complete Collection, not marked as owned.
I accidentally bought the Desperados III Season Pass even though it was included in the Digital Deluxe Edition which I already had.
I buy them individually. Why not also buy the collection?
I buy the collection. Why not also buy them individually?
The OST shows available to purchase to me as well. This happens with most game packages it seems.