Many old cars had the lock function built into the same handle inside. One rotation would open the door latch, the opposite direction would set the latch to lock. And I think all vehicles "back in the day" only used a exterior door lock cylinder on the passenger side. I know it was a law on the books here in Mass. to only enter/exit from the curbside door. Even into the 1980's it was still on the books. Maybe you already knew all this???