I've also seen the watch worn in the breast (hankie) pocket, tethered to the lapel buttonhole with either the chain or a leather strap, as a way to wear the pocket watch with a double-breasted jacket. Although vests were often worn under such jackets at one time (1920s-30s), it would have been tricky to access the vest pockets with the jackets buttoned, which they almost-always were. If you look at the "Jeeves and Wooster" TV show, you will see Bertie Wooster sporting his watch in this manner.

I have worn my pocket watch in the breast pocket of my double-breasted tweed suit as an experiment, but it was definitely tricky with my current watch chain. I find it easier to wear my wristwatch with the double-breasted suit, although I love wearing the pocket watch any time I wear a vest (I have a couple of 3-piece suits as well as a couple of kilt jacket/waistcoat pairings).

Andrew