it is impossible to verify the claim. If the claim were true, there would be no reason for the AD books to not be opened to select conference people, with appropriate agreements (e.g., non disclosure).

I suspect that in some years there has indeed been funding beyond the revenues generated by the athletic department through ticket sales and contributions. You have to realize that there are down years in ticket sales, down years in fund raising, and that the athletic department does not have any substantial endowment of its own. Consequently, in years of a deficit, there is funding provided by the university. University funds come from tithing. Therefore, the claim of "no tithing support" can be reasonably questioned.

But it is a spurious point. Other schools have state funding and general university funding. Private schools other than BYU have much higher tuition, which can be used to subsidize down years. The point is that all schools have the opportunity to use general allocations to supplement deficit years.