Complex sentence: The league started out in 1963 with 20 clubs which were reduced for the next season to 19 and from 1965 to 1974 there were always 18 teams in the league, except in 1972 when another season of 19 clubs was played.
Split into simpler sentences: The league started out in 1963 with 20 clubs which were reduced for the next season to 19. From 1965 to 1974, there were always 18 teams in the league, except in 1972 when another season of 19 clubs was played.