To demonstrate the point:
In an airline that I know, if a pilot crew member has slipped through the cracks and is discovered to not have a current medical , the flight may ultimately be delayed, 400 pax inconvenienced and put up at company expense in hotels until a pilot in the rank with a current medical can be found. The company had systems in place, but it was not totally idiot proof in that when someone wasn’t paying attention ( the pilot) and someone wasn’t doing their job (the system) , and the system caught up, there were consequences and one was that the flight didn’t proceed with a pilot who was not properly licensed.