Back when I was a child, women (aunts, and female friends of my parents) wore "slacks", with a zip on the left-hand side.
When I was a teenager, we used to buy jeans (which had a zip at the back, for some unknown reason), put them on back to front and then lie in the bath in them for a while until they moulded themselves to the wearer's shape.
None of the trousers, jeans, etc. that I now own has a zip anywhere but at the front. Some of them button left over right, some of them right over left. I heard somewhere that men's coats button left over right so that they can grasp their swords more easily if they need to defend themselves (or defend some unfortunate woman), but that is hardly relevant now.

None of my clothes smell of mothballs.