My current understanding, someone please correct me if I’m wrong:
Generated rookies with Superstar or better development may enter the league with Superstar abilities. Generated rookies with X-Factor development may enter the league with Superstar abilities and a Zone ability. In both cases, a player’s abilities can start out as locked. If locked, a player’s abilities are unlocked by playing that player a certain number of downs (500) and/or progressing to or above an OVR threshold.
In addition, players currently in the league who increase their development trait to Superstar or X-Factor - by completing Scenario Engine breakout scenarios or otherwise - may also earn and unlock Superstar and Zone abilities they did not previously have.