You can tell by Value what isn't a fastest trainer and you can tell by age. Therefore Max Value etc still applies its just not 100% once you hit capped values.

NordGens are players generated to maintain a healthy TM that are sold by teams such as AC Happy, FC Flaky, Shifty AC, FC Weakly etc (similar to starting team names) which appear a few hours after daily reset. Pick the Max Value ones.

The only way you know if a player is actually a NordGen player is if you click on the Team name in the mail you get after buying him and it will say "....Information not available...."