But they weren't in Geneva, they were in San Fran.
How can we tell? There is no dialogue mention of the location. There is no plot element to connect it with Starfleet Headquarters. The background in the establishing shot in "Demons" is generic water-and-green-hills. Could be Lake Geneva for all we know. The architecture is just generic Late Early Classic Futurism Retroed...
In any case, the first Geneva date was 1928, a real treaty on biological weapons. The second was indeed 2155, while the "Demons" meeting carries the date January 19, 2155.
I like my fan theory that the Klingons were actually signatories to the 2155 ban on bioweapons, following the Augment virus.
I like that one, too. <clicks "like">
Timo Saloniemi