Weren't Richie, Ralph and Potsie seniors for at least that long? It seems like it took a long time to get Richie to college.
The time continuum on the show is a weird thing. In the second season, there was an episode about the 1956 presidential race. So it would appear that first season a year earlier would have stretched back to 1955. So a 19-year difference between the actual year the episode was made and the year depicted. When the show ended in 1984, wasn't it supposed to be 1965? That's still a 19 year gap, so it was consistent in that regard. So if, over the course of ten actual years, the setting of the show also progressed ten years, how is is possible for Joanie to have stayed the same age for three years? That's pretty Twilight Zonish. And why was it that, in the later seasons, the show was taking place in the '60s, but the characters were dressed like the '80s?