Perhaps, but I'm not so sure that was the reason for the definition. For example, I know the dates of the solstices and equinoxes, and I'm (at best) a casual g

Perhaps, but I'm not so sure that was the reason for the definition. For example, I know the dates of the solstices and equinoxes, and I'm (at best) a casual gardener. The fact those dates don't align with what I think of as the start of the seasons doesn't prevent me from remembering them. In the location I do most of my growing, I'm actually more interested in tracking first and last frost - these are the primary constraints on many crops. These certainly don't align with equinoxes or solstices, let alone 1sts of months. Farmers, presumably, are even more intimately aware of the usual dates (and variances) for these events in their region. That's why I don't think it was the reason for labelling the solstice / equinox as the start of each season.