It's important to keep them on their toes.One day Aimee you're gonna stump them with your most awesome infraction hypothetical ever
Somebody can't be infracted for doing something that wasn't against the rules when they did it. If they are, that is a mistake and would be rectified.
However, if someone bumps an old thread in order to resurrect some earlier post that wasn't infractible at the time but is now infractible, that bump could be infractible if it was done for that purpose.