Trust me, any taxidermist will know.

Taxidermists always check the condition of hides, fur, skin, etc...

They need to to be sure the hide will tan properly. Taxidermists see plenty of legal animal hidesto know when something looks different.

It is VERY easy to tell if a fox was shot in the Summer or Winter.

Fur will either be prime or not.

I use to trap I was a kid. the fur dealers always knew if a fox was taken early in the season or later by how prime it was.

Spring/Summer fox will look skinny and fur thinner. Late Fall/Winter fox will have longer, thicker fur and thicker bushier tail.