Empire of the Petal Throne - City Occupants
The Empre of the Petal Throne was a setting developed and published in 1974, it uses a system slightly different than OD&D, but similar enough to consider. In this system everyone has certain skills (EPT 15): NPCs will have skills informing you of their occupation. Obviously, not a complete listing, but most that PCs may want to interact with. EPT divides NPCs into slaves and non-slaves. How likely will PCs encounter these different types of NPCs? Granted, these tables assume the PCs are actively looking for these types of people. To equate this to AD&D one could likely average the these tables.