For purposes of determining whether a child is eligible to be counted for the purpose of computing the amount of a grant award under section
7423 of this title, the membership of the child, or any parent or grandparent of the child, in a tribe or band of Indians (as so defined) may be established by proof other than an enrollment number, notwithstanding the availability of an enrollment number for a member of such tribe or band. Nothing in subsection (b) of this section shall be construed to require the furnishing of an enrollment number.