"swiss" designation

Very important question concerning the designation : "SWISS" or "SWISS MADE" on vintage watches. Why is it that one finds models of vintage Rolex, Longines, Omega, etc without the designation ? Does it ALWAYS mean that the dial has been re painted ? Is there an article on the history of this ? It is very important to us , collectors and thus every point would be greatly appreciated . Thank you .

Alexander, Paris.

Can't speak for Rolex, but many pre-WWII watches didn't have either at the bottom of the dial. Sometimes, it is on the dial but the tension ring or even the bezel hides it.

discussed where ?