In the grand scheme, Amazon probably doesn't know or care because the percentages are infinitesimal.
Amazon is to smart for that stuff anyway. Like during black friday, I made a bunch of orders because of their lightning deals. They grouped up some of them items. I didn't keep track of what, but likely the stuff that was in the same warehouse.
I've never had Amazon delay my orders because something was unavailable, even if I was using the free super saver shipping without Prime. Heck, one time, they shipped a .50 BNC connector thingy (needed as a filler) in it's own shipment.