So, the reason I suggested the 12/31/2017 banks statement is because of all the unreconciled deposits and charges going back to 2004. You have to get all those reconciled again and it would be too time consuming to try and reconcile every month since 2004. So, if you do one giant reconciliation from 2004 thru 12/31/17, that will get all those items reconciled so they don't keep showing up every time you go to reconcile a recent bank statement. In theory, since everything was reconciled, you should be able to reconcile 2004-2017 without much discrepancy. And, since your 2017 taxes are already filed, if you have to do an adjusting entry to get 2004-2017 reconcile just let your accountant know what happened and the adjusting entry you entered. With 2004-2017 transaction reconciled, you can move forward with 2018 monthly reconciliations and make sure those are correct as you prepare to file your 2018 taxes.
