Hello Ana,
The year end adjustment period is a special period available only when posting prior year transactions. It only adjusts the account balances for a period, not their "net posted" amounts.
Currently, you will not notice a change in your Income Statements (although we are considering making a change to this behaviour).
To see the change on the balances, open your Income Statement and change all occurrances of .Y to .BAL in the column. Then you'll see the difference if the button is pushed. Don't forget to save the statement with a different name.
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Andrew Bates