My thought was that the pilot occurred in the spring during 'pilot filming season' and that the time was made up at some point during the course of the first season so that S1 also ended in spring, specifically May. Given the taxes in Fly Hard [though Clark waiting until the last minute doesn't really seem in character - more like he'd have his ready to go as soon as he got the paperwork but whatever
], they were caught up by then. I forget which ep is considered the 'Christmas ep', not because of the plot line like the other three seasons but because there's some sort of decoration in the background. According to wikianswers [yeah I know] corn is often harvested in mid-late summer so the Corn Festival could be August or September. A gradual catch up kind of thing until Christmas?
Or no one just expected anyone to look at it so closely
.
