errors are rectified before preparation of trial balance:
To write the note for single effect error.
Errors are rectified after trial balance but before preparation of balance sheet.
To pass journal entry by using suspense account or write the note as method 1
In above both methods, two effect mistake, journal entry will be passed.
Errors are rectified in next year:
In preceding year, all income and expenses account are closed. Hence not possible to rectify respective accounts
But ultimately all income and expense accounts are transferred to trading, profit and loss account.
Hence in next year all income and expenses rectify through profit and loss adjustment account.