> That's not actually very common in non-profits.
there is a lot wrong with that assumption based on a single anecdote.
private foundations can have a single board member and that board member can be the single donor. although the IRS does not care in granting tax-exempt status, not all states offer a single board member for their own non-profit entity catalogue, but relevant states do like Delaware. of course Delaware does right? additionally, it doesn't matter what a state's non-profit entity selection has as any entity can obtain non-profit tax exempt status from the IRS technically, even unincorporated entities like sole-proprietorships ie. your general person when operating the charitable mission.
there is some transparency of this which is not aggregated, in the 990 series of tax disclosures that non-profits have to provide, this can show how many board members or directors there are, if that's whats important for you to prove. I don't think that's important, but this is about "common" or not and I don't have the aggregate data, that's where to get partial data.
none of these forms tell you the bylaws of the organization, these are still private documents. the bylaws dictate board member selection.
next, if Donor Advised Funds count as non-profits in your mind, that's a slam dunk as those are all pools of capital for grant making run by a single donor.
and where the transparency totally fails is in exempt non-profits, these report only the "postcard" 990-N and is entirely on an honor system that they have less than $50,000 in "annual receipts". these are cheap to create and nobody knows anything about them, what's actually on their balance sheet, there are basically no audits as they are tax exempt and there is no reason to determine what's missing.
I usually don't write this stuff as its more beneficial if the people had more disjointed opinions about tax matters, but I don't think Congress will ever reach consensus on any opinion people harbor so its fine. One of those examples where truth is less familiar than fiction.