The official write-off amount of $2 is ridiculous, too. If the government overpays by a few dollars, who cares? It's going to Canadians, and the cost to track it down isn't worth pursuing. It should be $10, imho, and anything less than $100 (or maybe even $500) should just get a notice that there was an overpayment, and next year's amounts will be reduced by $x÷4 per quarter.

The interest on even $500 for a year is negligible compared to the direct cost in labour and external cost of wasted time to correct the error. Just roll it into the next year's benefits totals and move on.