From what I know, not all schools have Index #s, first of all ... and of the ones that do, almost none will cop to using them as a definitive cutoff. They basically use the numbers, I think, to stack people's files in order of "Almost Definite/Unless Mass Murderer - 10 sec review" / "Maybe, We Actually Need to Read the File - 10 min review" and / "Almost Absolutely Not/Unless Prez of the USA - 10 sec review" ... or something like that.
At least, that's what I've read/heard.