When I have multiple containers, I tend to test just one of them, unless I'm really interested in differences. I also test when I rack and I try to blend the containers when I rack, so I guess that gives an average of sorts. If I have different lots for a reason like different Malo, yeast or other additions, I test each - cause after all, I'm looking for differences.
Sale o is right about tasting, I do try to taste each container. Nothing worse than to blend a compromised jug into a sound carboy