Yes open face lever set watches were very common. From 1893 on all Railroad watches that were “Approved For Railroad Service” were required to be open face, screw on bezel and lever set.
It sounds like the case is original to the movement. The standard procedure well into the 1920s when purchasing a pocket watch was for a customer to choose the movement and have it fitted by the jeweler to a case of choice. Many of the case companies like Star machined a lever slot in the case even though it was also set up as a pendant set case. This way a jeweler didn’t need to keep both types of cases in inventory and or it saved him having to cut a slot himself if he didn’t have both types on hand.
Hope this helps Fred,