Hi Peter,
keeping those old batch input session in the system is
1/ risk because some one can process them and maybe they are already not needed. So it may cause you inconsistency in your system.
2/ Best approach is to go session by session contact responsible user/requestor from business of the data and ask him what shall be done with it.
3/ From governance point of view an organization should have an rule in place (kind of house keeping task) that those batch input session are reviewed on regular basis and appropriate task is taken within reasonable time frame.
cheers
m./