I don't undrerstand the reveal in Season 2, where... (look inside!)

... because of spoilers obviously.

So MacKenzie sits down and watches the raw footage of Jerry's interview with the general, and has that brilliant revelation about the shot clock... Except that shouldn't be possible. In an earlier scene, we see Jerry forging the raw footage, and he is using a video editing software with which he crops the area around the general - at the time I thought this was shown exactly to let the audience know that Jerry is covering all the bases: he is expecting the TV to be a problematic element in the shot, so he crops the general so he can manipulate that part of the image.

The TV is clearly outside of the area he has cropped, so with this manipulation, Jerry is free to edit the general without affecting the TV, thus without affecting the shot clock, so MacKenzie has no chance of revealing the manipulation.

Did I miss something here? It's been bothering me since I saw that episode and I haven't read an explanation to this yet. I remember, I felt very uncomfortable when earlier in the episode Will and Mac are discussing the shot clock, and I thought to myself: "Hey, hey, hey, you have already shown Jerry cutting around the general, so you can't go that way anymore!".

Can someone explain why despite the cropping such reveal was possible for MacKenzie?

I was looking back to see if you were looking back at me to see me looking back at you