"Montana plays loosie-goosey with selling death certificates"

I don't know why you assumed that State. Most of the deaths I have dealt with were in CA. I would recommend you get at least 4, because you end up sending them in or leaving them as proof for agencies and banks to have on file, or mail in for closing accounts or canceling services.

"On the other hand, in Arizona you can be appointed personal representative with just an affidavit; a death certificate isn't required."

Which makes my point, that having a death certificate does not mean that person is handling the estate and has the right to have anyone take any action, including tax filing, on behalf of the deceased. A death certificate is not proof of authority. It's proof of the death.