I have seen a 1972 Maverick factory AC car with the cowl vent on the driver's side. It had the fresh air vent installed on the driver's side. I would say only the 1970-early 1973 cars could have possible came this way (due to the routing of the vents/hoses on 1973-1977 cars).
My green 73 is about as early as we've seen yet, and the drivers side is sealed up, now my brown 73 is late, but I haven't looked at it to see.