As 'Interested Insurer' they would have been directed by the Motor Insurer's Bureau to deal with any third party claim and they'd also know damned well that having banked a cheque for renewal of an existing policy, they'd have had to deal with the rest as well, or be dragged before the civil courts.
Technically, they are not allowed to back-date a cover note or certificate but if you'd had to 'produce', the underwriter would have had to provide a letter of indemnity confirming that they would have dealt with any claim.
It's obviously best to be in order with the paperwork, but in effect, he's had two month's free cover.