Trial Balance and Errors, Kaplan Exam Kit question

The draft financial statements of Haseen’s business for the year ended 31 July 20X0 show a profit of $54,250 prior to the correction of the following errors: 1 Cash drawings of $250 have not been accounted for. 2 Debts amounting to $420, which were provided against in full during the year, should have been written off as irrecoverable. 3 Rental income of $300 has been classified as interest income. 4 On the last day of the accounting period, $200 in cash was received from a credit customer, but no accounting entries have been made. What is Haseen’s profit for the year ended 31 July 20X2 after the correction of the errors? the answer of the book says that there is no effect, because there was already an allowance created and $420 was written off as expanse. But should'nt we write off the expense at the end of the year by crediting receivables and debiting irrecoverable debts expense, and then separately adjusting the allowance account, even though this amount was written off as expense? I came to the same answer but with different approach, and i am confused.