However, I don't think that will satisfy the school.  Just because a person did not file a tax return, does not mean that person was not required to file a tax return.

It is quite possible the school will still want a tax return for that parent.  That parent may need to file a tax return (with zero income) to satisfy the financial aid department.
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Did you live with that parent?

I don't think you need to spend money to prepare a tax return with zero income.

Yes, they now live with that parent.

So I am guessing the 4506-T is attached to their Social Security Number and should show they have never filed?

However, the letter does not state whether that person SHOULD have filed.

If they never file then the IRS would have no record of course, since there is no record.   All the IRS can tell you is what you already know, then the IRS has no record of filing.