Complex sentence: Since the 1942-43 season, there had only been six team in the NHL, but this was to be the last season of the "Original Six" as six more teams were added for the 1967-68 season.
Split into simpler sentences: Since the 1942-43 season, there had only been six team in the NHL. This was the last season of the "Original Six" as six more teams would be added for the 1967-68 season.