When asked how CRA's position - that a debt must be unrecoverable in its entirety before it could qualify as a bad debt under s. 50(1) - could be reconciled with CRA's position that a partly bad debt could be deducted under s. 20(1)(p), CRA stated (TaxInterpretations translation):
[T]he concept of debts in subparagraph 20(1)(p)(i) can refer to each account receivable of the taxpayer. Thus, following a diligent examination of the facts, certain of the amounts due by a customer can become uncollectible and these represent the portion of the debt which has become uncollectible.
On the other hand:
A debt can be eligible for the election under subsection 50(1) if it is uncollectible in its entirety at the end of a taxation year. Note that if a debt described in paragraph 50(1)(a) is settled in part and the creditor establishes that the balance owing is uncollectible, an election under subsection 50(1) could be made with respect to the uncollectible portion.