Series 1 & Series 2 manufacturing date confusion

Studying the Club Register Statistical Data  http://vwgolfmk1.org.uk/index.php?page=car_register&type=stat  I was confused as to series 1 hatchback being listed until 1983 and the series 2 listed from 1980??????  Surely they were not manufactured at the same time???????  Just trying to make sense of the statistics.

Does anyone know how many cars are in the club??