I've just looked that up, it was around 1950, if I'm not mistaken. How many teams did that before Spurs then? I think we can safely say it doesn't happen often, especially when you bear in mind that 3 teams are promoted every season and all 3 fail to win the league in the modern day, I'm not sure whether it was always 3 teams.
Mind you, with a squad of 5* players from the previous season, it's possible to win the new league with 4* players and a few 5* players from those that hit 6* the last season, especially at the lower levels.