The following information is available for Quality Book Sales's sales on account and accounts receivable: Accounts Receivable Balance, January 1, Year 2 $78,500
Allowance for Doubtful Accounts, January 1, Year 2 4,710
Sales on Account, Year 2 550,000
Collections of Accounts Receivable, Year 2 556,000

After several collection attempts, Quality Book Sales wrote off $2,850 of accounts that could not be collected.

Required:
Explain why the uncollectible accounts expense amount is different from the amount that was written off as uncollectible.