Man, I don't even want to think about it. I'll just give you an example:
I bought Batman Arkham Asylum for PS3.
Right before Arkham City came out, I bought the 360 version.
When I bought Arkham City for Xbox 360, it came with a free version of Arkham Asylum.
I then bought Arkham City for the Wii U.
I bought Arkham Origins for the Wii U but it was missing some features.
I bought Arkham Origins for PS3 since it was the best version.
I bought Arkham Knight for PS4.
I then bought Return to Arkham on PS4.
There was an amazing sale in Return to Arkham so I bought it again on Xbox One.
Arkham Origins became backwards comp so I bought it again on Xbox One.
I wanted the whole series on one console so I bought Arkham Knight on Xbox One.
And somewhere in there, I bought the digital version of Arkham Knight PS4 even though I had the physical version. So.. yeah.