I'm 99% certain that I never saw a Swiss-threaded Shimano bottom bracket. Even finding a French threaded one was tough in the '80's and your chances diminished as "French" bicycles were increasingly made in Taiwan.

The way to check is by looking at the fixed cup. If French thread, it'll be right-hand threaded (and prone to working loose). If really Swiss thread, the fixed cup will be left-hand threaded.