You request the suspension log from the council. This will give the relevant dates. However, this would delay your reps, so best to submit reps on the basis that your car was legally parked on <date>, and on this date, being familiar with the local parking arrangements, and regular suspensions taking place, you checked your car just before travelling for a short stay abroad, and no suspension sign was seen. Therefore insufficient notice was given of the suspension, and as a resident, you consider the PCNs should therefore be cancelled.