I don't think that it is clear what point is trying to be made here. That the NIP's were served out of time and therefore invalid?
That is a difficult defence at the best of times. When these things are challenged, courts are presented with comprehensive evidence of the administrative systems used to handle these documents. If you had a statement from the Manager of your local delivery office categorically stating that no post was delivered during say a two week period due to staff shortages then it would be worth giving it a try but short of that or something similar, you will be very much fighting an uphill battle regarding NIP invalidity.
At the end of the day, your statement :
He received 2 NIPS followed by 2 FPN’s.
...seems pretty ordinary and straightforward.