How does the people in Planetos know what a year is?

Ancient real life societies didn't know what a year was because they knew the Earth was spinning around the sun once every 365 days. They thought the Earth was the center of the universe and the sun was spinning around us. Every ancient/medieval society that ever existed on Earth always knew what a year was because of the passing of the seasons. If you started the year at the coldest moment of the year, when you have already passed the hot season and go back into the cold one, a year had passed. It was the exact same cycle on almost every place on the planet since long before humans existed. You couldn't miss on that.

Then how do people in Westeros know what a YEAR is? The seasons cycle in this world is completely wonky and does not align with the translation of the Earth around the globe.

It could be explained that the masters of the citadel are so advanced in astronomy that they've learned about the Earth spinning around the sun once a set number of days, and that they've shared their knowledge to everyone in the seven kingdoms, and that everyone in that blackwater realm has accepted that nonsensic tomfoolery about the Earth spinning around the sun, but even if this is true, how do other societies like the dothraki know what a year is?

In a world with no seasons or seasons that can't be predicted, the concept of a year should not exist as we know it, and the most likely scenario is that every society/civilization would measure long time cycles in different ways.