The subject of distilling seasons came up on another thread and I thought it worth discussing. In the days before air conditioning (which the kids date somewhere between the neolithic and bronze ages) late Summer heat had a decided effect on distilling. Yeast would grow lethargic in the mash tub, even lay down and die on the job, even the stills worked differently. So the plants simply shut down during the months of July-August which had the practical advantage of allowing time for maintenance, barrel rotation and other necessary upkeep. This broke the distilling time into 'seasons' between Sept-June then picking back up in September. This means that during a calendar year (Jan-Jan) there would be parts of two different seasons.
Interesting that a requirement of bottled in bond was the whisky had to be produced in one season even though one season actually took place in two different years.