Actually income accounts usually start with a zero balance.
Balace sheet accounts start with a >$0 value.

But for income statement accounts (excluding Retained Earnings),
there is generally a method to insert prior month's figures into
the Chart of Accounts.

>Accounting packages should all ( according to standard accounting practices ) have some method of recording initial / starting balances, since these numbers do exist and no software developer should presume that their potential customers are starting at $0.00 in all accounts.