No, all cars did not have cabin filters years ago. You may get a stray dried leave or too. No big deal. My wife drives a 2014 Rav4 and we live in the Minneapolis area. Last year we never saw an issue. But I don't drive it. I assume you did testing with a new cabin filter and without and you saw a difference? Also you need to take in account too much air flow over the heater core that you actually get a reduced duct temperature. I have owned cars years ago when there was no cabin filters where the heater core was too small and setting the fan speed on high reduce the temp so much it was warmer one click down .