The first generation of forecast models (on computers of that era) took one day to arrive at a twelve hour forecast. So after the fact forecasts made no sense.
So what changed? Super computers ( often networked computers) could crunch huge amounts of data very fast. A six hour forecast produced in five minutes. Now the National Weather Service and separately NOAA have huge processing centers in Maryland, Colorado and I believe in Oklahoma. Each specializes, one in forecasts, one in severe weather and one in research.
