It may not have been very sunny. I usually think of sunny 16 being based off of the sun at noon. Obviously in the morning and in the evening, even if the sun is visible in a clear sky - there's going to be less light falling on things. That may have been the case with you?
This was shot at 9AM: and I used f5.6 even though the sky was clear and the sun was visible
Anyway here's some more old guides:
Kodachrome (1950s I think)
Ansco and Kodak films, circa 1952
Cee-Ay 35 booklet, 1949.