I thought you might be interested in looking at Can I install Arma 2: Reinforcements with Arma 2 vanilla alone? Do I need Arma 2 OA?.
https://forums.bohemia.net/forums/topic/123926-can-i-install-arma-2-reinforcements-with-arma-2-vanilla-alone-do-i-need-arma-2-oa/?do=findComment&comment=2053638
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