What year did self canceling turn signals make their debut. I have a 67 that does not have them and I don't know if they were not available or they are just not working.
Pull the steering wheel. The rocker on the switch is plastic and both sides may be broken off. Especally if the switch got stuck and stopped moving, then the wheel being turned will break them off. THere is a ring with the canceling pins that is a friction fit on the bottom underside of the steering wheel-may have fallen off. Note sure if that's accurate for a 67, I'm fairly sure that's what's on a 66...but your car should have canceling signals.
From the internet: http://www.motorera.com/history/hist11.htm
Another noteworthy lighting feature that started as an accessory and ended up as a necessity was the flashing turn signal, introduced by the Protex Safety Signal Co. in 1920. But the idea was proposed (sort of) in 1916 when C. H. Thomas of Norristown, PA, wrote to Popular Mechanics describing an invention -- a battery and electric bulb attached to a glove so drivers could see hand signals at night.
Flashing turn signals were first offered as an option by Buick in 1938, but only as rear flashing lights. In 1940 the flashing signal was extended to front lights, and the signal switch was given a self-canceling feature.