Could Have Not Been?

However, the negative of this generally means simple lack of ability or potential, and not fate: Larry could not have been (or simply could not be) the one who robbed that bank yesterday. He's on vacation in Belize.

Could not be Vs could not have been?

It's a very subtle difference. "Could not have" is used to definitively declare that an impossibility occurred in the past. As in, it was impossible for the person to be reached. ... "Could not be" expresses that an attempt was made by the writer to reach the person, but it was unsuccessful.

What is the meaning of have not been?

"Have not been started yet", using persent perfect in passive voice, is useful when you emphasize the present state of things connected to the past (the courses were announced in the past, but not started yet at present), and imply that someone should actively start the courses.