Why does the ShouldersAccessory property have an S in the HumanoidDescription?

In the HumanoidDescription, there is a property named ShouldersAccessory which takes in IDs of shoulder accessories.

In the AssetType enum, however, shoulder accessories are called ShoulderAccessory, without an s

I know that the AssetType enum doesn’t exactly correlate with the humanoid description properties (take hats for example) but this seems to be the only instance where the name for shoulder accesories has an s.

If you take hats for example, the AssetType is called “Hat”, meanwhile the humanoid description is called “HatAccessory”. I assume this is because all accessories used to use the Hat AssetType, and the other AssetTypes were introduced later (judging by the value).

But is there a reason why the shoulder accessories have an s in the humanoid description and not anywhere else?

My theory is that the property in the humanoid description was introduced before the unique AssetTypes, but I don’t have a way of verifying this.

This is just something I found interesting, and not really something I need help with, but maybe someone here knows the answer.