Cross progression: Currently playing on multiple platforms?

I don’t think I’ve seen this answered before. With cross progression, your unlocks will carry over from one system to another, like between your PC and consoles. But what about people who already own the game on different platforms, and have their BNET account linked? Will you get a combination of your unlocks from both? How will duplicates be handled? I have the pink Mercy skin on both the PC and the Xbox, what happens there?

I believe I saw that you can transfer cosmetics from previous accounts to your current one, but I’m not even like 60% sure. Really hope this is the case as I played on Xbox for the majority of my Overwatch playtime.