You should take readings from Sylvain, Hilda, and Claude - since Sylvain is from a different Fodlan than at least Hilda and Claude, it would be useful to identify an overall 'Fodlan' signature. If you collect data from Summoned from a single timeline in a world, there's no guarantee that the signature wouldn't be specific to a single timeline rather than the world as a whole. Myself as well, although I am more difficult to access. Any cases where Summoned come from more than one timeline will be helpful to measure.

I think that line of thinking is well worth pursuing.