Thank you for posting in the Community. I'm here to help guide you in the right direction in reconciling your Petty Cash account.
Since the transactions were from previous years, you can reconcile them without having to do so one month at a time. The recommended method to reconcile them is one year at a time.
You can refer to this article for more information: Reconcile an account for multiple months or years of transactions and financial statements.
Before doing the reconciliation, it'd be best to consult your accountant first to verify if this is the best method you can use to reconcile statements and transactions.
If you need some related articles in the future, please feel free to visit our site: Help articles for QuickBooks Desktop.
Keep me posted if you have additional questions about the reconciliation process. I'm always here to help you further.