Okay, so I have both Fallout 3 (All expansions bought separately) and Fallout: New Vegas (Ultimate Edition)
Both on Steam, but here is the thing, I have them on different accounts.
I bought Fallout 3 a couple of years back, on my old Steam account, I still have it installed.
I bought Fallout: New Vegas last week, on my new Steam account.
The question is, will TTW still work even though both games are on different accounts?
Or will I need to buy Fallout 3 again?