Mostly in the late 1920s, thus matching with how I phrased it above, at post #14. This is why I used the qualifier 'ceteris paribus' above. Both Uruguay as well as Hungary were almost as close as full-professionalism as you can get; training as a professional and not in the evening hours. With the national team also becoming a sort of club team, or globe-trotting attraction (Uruguay's Tour around Europe), and having them at your disposal for a long period of time. Hungary already the used the 'booster' to have a core located for many years at one club (and then not just for two/three years playing together, like for ex. Rep and Neeskens had by 1974, but for a prolonged period of time).