Thoughts from an extract brewer;
I think it would be interesting to buy a beer "Kit" in a box and then also buy the exact same as individual ingredients. Then check for dates on said products, brew side by side, might tell us a lot, maybe nothing. That said, I'm sure the big outfits know how DME, hops etc ages. They probably do the best they can to insure even the box kits don't gather too much dust. Some places even claim they make their kits only when ordered.
I haven't seen anyone on HBT that claims to works at (or did) one of these places. Probably is but they don't dare say that they do, the "incoming rounds" would be huge I'm sure.
Also I smoke so I'm sure I miss some flavors that non smokers would call glaring faults.
I know that there is little actual substance in this post Some times I just rattle on,,,
Cheers,
Joel B.