Where to Enter Bad Debt

If they are truly "uncollectible" and they have not already been expensed, enter the write off balance into the "one-time, non-operating revenue" line item at the bottom of the income statement entries.  This will serve to reduce the effective profits/SDE by that amount and adjust the valuation accordingly.

Every company does their accounting in their own manner and may use cash basis or accrual basis, which would impact whether or not there needs to be an adjustment.

For now - I would go with my first paragraph as the proper entry.  If these bad A/R stretch out over two periods (the sales were made in two different periods), they the amount should be split between the current year and the prior year (into the one-time,non-operating revenue line items)