How do colleges know how many AP's you took?

How do colleges know how many AP classes you took? I often see that schools list the average number of AP classes taken by their admitted students for the class profile, but does that include senior AP classes? I am just confused as to how senior AP classes play into admission (early) since they aren’t listed on your transcript and colleges have no way of knowing what your senior course load is.

I know that you have to list all your AP exam scores and future AP exam dates on common app, is this how?

Many apps ask what your senior courseload is.

Many colleges request first quarter or semester grades for senior year as well.

No, you don’t have to; it’s optional. However, you do list your senior year courses.