A shot of the deployant on one of my JLCs I think you could tell the period from its style, I've always got on with this version as intuitive to use& comfortable. When I've tried newer ones with a butterfly style I struggle somewhat - sure I'd get use it ...
The one I was referring to has been out for a couple years already. It's a two winged deployment clasp, but it's well built, sturdy, and you can completely remove it from a leather strap with no tools! And you don't need a special strap, it just requires ...