Yeah, that is what I thought and had to go double check myself, because I was honestly unclear of the timing.
Okay Genenva mostly deals with how you treat other soldiers during combat (not shooting medics for example), how they are treated when captured, how you treat civilians when you take over their town, what is allowed to do to get information, what is not allowed to do to get information, etc.
You are talking about the St. Petersburg Declaration of 1868, which later became absorbed into the Hague Convention of 1899 and later 1907
This is where you can read about use of hollow point bullets and the use of large caliber 12.7mm / .50 cal in use against anti-material targets (humans) and things like poison gas and horrible things people came up with to kill each other.
They are thought to have been rolled into the Geneva Convention, but that is not the case, though I believe the same world court that would hear a case about one, would hear a case about the other. Though I am admittedly no expert on the matter.