Pre-accumulated data is calculated by a balance from either, the previous year (closing balance) or opening balance when you begin a new account.
The opening/closing balance works as a starting point and every time you run payroll the amounts add on top of the balance.
Example: Opening Balance + Payrun 1 + Payrun 2 + Payrun 3 = Total. Totals can be annual leave, personal leave, long service, net earnings and so on