Man, I think I'm probably missing out something big time but isn't D# in Cm scale which is also Eb, right? But in F major scale there is no B, there is not that white note between A and C used in the scale but still it would be ok to use it when using C major 7 chord? Maybe it's something that I don't get with the sharps and flats...?
See? How could C Major 7 fit F Major scale?
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And I mean it works, the C Major 7 works great in the progression, but why is it?