Don't be so sure. They just process lots of forms and have standard excuses in the hope that people accept the penalty offer.
I refused an offer a few months ago, as the posted speed limit was contradictory and that's why I was over the limit when I passed the camera (I'd never driven down that stretch before). Now I'm holding on to photographic evidence indefinitely, sitting around to see if they get round to prosecuting me.
No sign yet.