If it weren't or hadn't

Hi,

Could you tell me if my interpretation of these sentences is correct?

1) "If it weren't for them, we could have had the exam in June." Now we can't because they (our classmates) asked the teacher to schedule it for the last week of May.

In this case, I used 'could have had' to emphasise that the teacher's already made her decision and there's no way we can convince her otherwise even though it's still May.

2) "If it hadn't been for them, we could have had the exam in June."

This one would probably be used if I was referring to a distant past.

3) "If it weren't for them, we could have the exam in June."

This one focuses more on the present.

I still think that all of them are correct.

Thank you.