On zip codes, they are somewhat by population, but not strictly. Most likely the way to identify where the pesticides were pulled would be by township and section numbers. Although I would be surprised if the Irig farm is more than one section (640 acres), it might fall within multiple sections. To make things more fun you can actually explain this issue without changing the story. Since it is Lois narrating it, we just write off the problem as Lois having harrd "section numbers" but thought "zip codes, that is what a bunch of numbers identicating location are". Lois, as a total city girl assumes there are a bunch of zip codes involved, and that must be what the numbers she is dealing with are.
It is totally workable for me for this to be after HiM but before PML. Some of Clark's dialogue in HiM works better if it is before PML. Also, since in HiM the bad guys are using a December 1993 calendar, this makes everything fit well with the story. I was actually gald you mentioned HiM, because before that I was even more at a loss why Lois was talking about a rematch with Clark.
