As you say, the inherent issue with any automated system is GIGO, garbage in-garbage out. As you note, the basic system, for a single league, would be easy…make it for all professional leagues, and it’s suddenly quite complex…make it for all SFA regulated leagues, it’s a nightmare.
Lets design this system on paper:
1) This system must track all registered players at least by name, birthdate, place of birth, current and prior clubs and (likely) other characteristics (likely already in place, but would probably have to be transitioned to a new system)…plus comply with GDPR and avoid fines…which is always fun because, how long do you keep a free agent in the system?
2) This system must input all player transactions in less than 2 days (games occur 3-7+ days apart).
3) The system must input all disciplinary or eligibility actions in less than 2 days (knock on effect is requiring officials to enter disciplinary data into a system within a day).
4) The system must be programmed to evaluate the input data and sort based upon league(s) in which action occurs, the individual rules applied to that league(s), the effects of transition between leagues and registration regimes, etc.
5) The system must be easily accessible by officials and clubs…while being absolutely secure from hacking or intrusion…and must be able to return results for an enquiry within a minute or less.
…While all this happens, if Madge (entering data for the SFA) checks the wrong box for the card that Steven issued to Jock (checks not violent conduct instead of violent conduct, perhaps), then the system tells Clarance that Jock is eligible to play against United, but Peter notices Jock playing and thinks, wait, he’s not eligible…