It wasn't even always that complicated, it is easy to observe the seasons. You always know what season it is because you know what the last season was. You are going to know winter is on its way just based on however many years you have observed it. It wouldn't be like people who didn't keep track of years wouldn't know to prepare for winter. Then you have things like the zodiac, where they simply observed where the sun was in relation to the stars behind it and drew significance with what that might have meant based on the season and significant climate or weather events and so on.