Singular: %d identical back-in-stock notification was sent to the same customer recently. This time, we skipped it to prevent spamming.%d identical back-in-stock notification was sent to the same customer recently. This time, we skipped it to prevent spamming.
Plural: %d identical back-in-stock notifications were sent to the same customers recently. This time, we skipped them to prevent spamming.%d identical back-in-stock notifications were sent to the same customers recently. This time, we skipped them to prevent spamming.