As Emily said, you can change the closed account date to make any changes retroactively. However, this will impact your books and accounts from 2016 onward. This can get very complicated during tax season.
Do you know who did the books before? They may have done the reconciliation by hand/outside the program from 2014 and not said anything. I'd check with them before making any permanent changes.
Also, if the account is showing $0 balance, does this mean that those charges entered from 2014 have already been balanced? Or we they never entered?