By default, the system optimizes for speed and doesn't ensure that seller A's customers get the units sent by seller A and B's customers get those sent by B. This means that in a discussion about provenance of specific units, this is a distinction without a difference (or alternatively, all units of a product are in one area, which isn't necessarily physically contiguous in space).

Yes, my point is irrelevant to the main discussion about commingling.

I was commenting only because most people make the same false assumption (that all units of X in warehouse Y are stored together) and find the random stow model interesting when told about it.