Summer, spring, autumn and winter textures/skins are meant to display depending on the time of year (season). Snow is meant to be controlled separately, depending not on season but only on whether the asset is above or below the snowline setting.
Assets regarded as “seasonal” may have all or only some of those attributes, depending on what is appropriate. An evergreen tree or an inanimate object like a building, vehicle or a body of water might only have a regular skin (same in all seasons) plus a snow skin and still be referred to as a seasonal asset. Other things like deciduous trees could have skins for all 4 seasons, plus snow.
If you’re lucky, the seasonal details might by fully explained in the asset’s Description, but often the only ways to really know are by examining the contents of the asset’s config.txt file (season-selector tag) or by experimenting with the asset in the game.
Note that in some seasonal tree assets, the winter skin has been made snowy. This is really a modelling error because it does not allow for situations where the winter is not always snowy.
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