TfL only ever *charges* one offence but others may be taken into consideration. if no pattern can be detected, it's unlikely they will make other allegations. But that is all a bit premature at the moment.Did your Dad also use the card? In which case, how will the OP's usage be detected from the Dad's usage, especially if neither were regular 9 - 5 commuters?
If they can't determine who used the cards on any particular occasion, then presumable the OP can only be charged with a single offence, i.e. when he was caught.