If you want to see the reports for the previous year you will create Opening Balance by entering the closing date of the financial year For this, you need to add the Retained Earnings individually that is income and expense accounts will be entered separately.
Say Paula Walker need to create the opening balance as of 2016, then:
The Date will be previous year instead of 2017.
Account balances for the Income and Expense for the previous year will be entered separately from the Trial Balance that will appear under Current Year Earnings in the Balance Sheet.
If you enter the Income and Expense Account Balances while entering Opening Balance, you will be able to see the Current Year Earnings in the Balance Sheet.
P&L will show previous year data too. If you have entered the income & expense types of chart of accounts, then only P&L will be visible.