It's possible, but this is about probabilities and we're looking at two:
Did the cameras capture the December trip? If so, why wasn't a PCN issued e.g. the process of comparison of VRM and TfL database showed no violation etc?
Could this same misread as regards camera data and database be responsible for the March PCN?
In any event, IMO the Dec. events would allow them the defence of legitimate expectation. OK, if this defence is used then the burden falls on the keeper, but it wouldn't be difficult to prove the December flight, that they only have one car and to set out their route into the zone etc.