Okay Alex, so I have the detail from the hire company - they were quite efficient and helpful actually.
It seems that the hire company logged receipt of the original NIP to themselves on the 14/07/15 (very recently and almost 3 months after the offence) and responded with my details that same day. Strangely, the Police who had taken 3 months to process the initial NIP to them then only took 3 days to send a new NIP to me - dated the 17/7/2015.
The hire company advised me that the relevant date is that on which the NIP was issued to me and not the date of the alleged offence and that in their view the previous correspondence/NIP to them was irrelevant, but agreed it was an inordinately long time between the incident ad the police issuing the first NIP.
They advised that I call South Yorkshire police and discuss the case, which I did, but there is no capacity on this answer service line to discuss anything to do with camera cases - only those where an officer was involved. This info line advises that I must request a copy of the photo or any more information in writing.
So, as the hire company seem to be indicating that as I personally received this NIP within 14 days of the police learning of my direct contact details, then it may actually be valid, even though they were so very slow in sending the initial NIP. Is this correct?
If it is correct, then what what should I do now? I have to complete the NIP and return it today (or at latest by 31/7) and would like to include a letter of appeal that the NIP was really received very late in the day, so it is hard to remember events precisely (as I thought I was driving within the legal limits) and that it was a very marginal speeding offence on a clean licence in a strange car and city with no intention to drive dangerously.
What do you think? Will that achieve anything, or will it make things worse?