I think for the purpose of my 52 game challenge, ill just note when I beat each difficulty.
For the 52 game challenge, me personally, I would consider it under 1 of 2.
If I'm just playing multiplayer with folks, when I'm done it is "beat"
If I'm playing by myself, I'd consider it beat if the credits pop, but I'll probably work towards 100%, but if I abandon before 100%, it's still beat.