Opening the individual pay cheques to view the stubs is the built-in way the system tracks past balances.
If you need to calculate historical balances for all employees without opening each pay stub, you can use a manual spreadsheet workaround. Go to the Reports menu, run the current Vacation and Sick Leave report, and export it to Excel.
Then, run Payroll Details report for the date range starting the day after your year-end up to today. By entering those into Excel, you can calculate today's balance by subtracting the vacation accrued since year-end, and adding back any vacation taken.
Let me know if you need anything else.
