NIC1A return penalty

This happend a year or so ago with P35s and now a client has received a £400 penalty demand for not filing an NIC1A return.

It is actually correct that no NIC1A return was filed but the P11Ds were filed in May and there wa no NIC1A to pay - so the client didn't file a return.

Does that mean there is still a penalty?

And if so (and actually even if not so) why does HMRC wait until November to tell them they are late? If they waited until Christmas they could claim another £200!
Greg