I'm rewiring my house, and keeping some circa 1920 light switches, which don't have ground screws. The switch cases are porcelain, and have a brass yoke. I originally planned to sandwich a ground pigtail between the yoke and the box, but since the metal box itself is grounded, I figure the yoke will already be grounded to the box via the mounting screw. Is it necessary to pigtail a ground wire directly to the yoke, or would they just add clutter to the box?
I would not worry about adding a “wire” to the switch either the box grounded those nice bright brass yokes being connected to the metal box will be more than enough grounding (in the US it is code compliant to use this same method with some devices). Your switches look to be in exceptional condition I hope the contacts are also if so they may last another 100 years.