I noticed it comes with purchases of the the three Fallout games, but will owners the Fallout games from the days of Interplay get Arena and Daggerfall added to their account?

Not a big deal if no, but I'm just curious.

Why would we? When I got Fallout games from here they weren't under Bethesda

Ignore what I said. I thought the versions I had were updated to the Bethsoft versions and they are not, it seems. Which is fine :)

So that answer would be no, Arena and Daggerfall aren't included because the old games aren't the New versions. They are 'classic.' For the time being.