I'm going to take a guess and say that this is their first year of implementation so that they are going a bit overboard in documenting that you are immaterial. Even if they know you are immaterial, they're smart to cover their butts and document that the first time around.
However....the request still seems excessive. I think it is reasonable for them to ask for your charter and bylaws and filed 990; those give them the proof that you are independent, and that you are immaterial. That other stuff is busywork.
Did they say why they wouldn't budge? It seems you have two options here, and it sort of depends on your relationship with the school.
1) Just cave and give them what they want. You have nothing to hide anyway; your principal has probably already seen most of the reports that they want. Of course, it will take some extra volunteer hours to pull it all together, but it shouldn't be that bad.
2) Resist with a nice letter. There is an excellent example of a letter to send for exactly this situation on page 4 here:
www.mnpta.org/VoiceMarchApril2005.pdf
You can't use it exactly as written, because some of the PTA stuff doesn't necessarily apply in your case, but you could ship it off with the 990, copy of bylaws and charter.
Good luck!