Wow, great collection! I'm fairly confident that none of these cels are sketches are fake. I've seen and bought a ton in my day and these all look genuine. It looks like you bought several of them from icollect-online who I know purchased multitudes of boxes directly from the studio, so there's no doubt about their authenticity.
Generally artists won't fake cels unless there's a good profit margin to be made. Faking cels takes a lot of time, research, and effort. They're only going to be faking cels worth several hundred dollars. Additionally, they tend to target more popular series, like Evangelion, Dragon Ball, Sailor Moon, etc.