It reduces logistical volume of the shipped product I think was the rationale. Not sure about the other questions.
a 5 dose vial with 7 doses volume means an error of 40% .
the final bottling process is not obvious, so
H1: the stock concentration could _possibly_ be diluted by up to 40% in some vials.
H0: the vials are filled in one aliquot of appropriate concentration at higher volume.
bare minimum this is sloppy manufacture, due to deviation in portion control.
worst case 7 people are receiving off lable dosages.