The purpose of a notice of intended prosecution (NIP) is to inform a potential defendant that they may be prosecuted for an offence they have committed, whilst the incident is still fresh in their memory.
When you receive a NIP it doesn't automatically mean that you are going to face prosecution, it is a warning that you may face prosecution.
The NIP must be served on the driver or registered keeper within 14 days of the offence otherwise the offence cannot proceed at court. If the details of the driver are not known, then it is sent to the registered keeper. In either case, so long as it arrives at the relevant address within the time limit the notice is valid.
If the registered keeper has changed address/not informed DVLA etc., as long as the NIP arrived at the address on record for the registered keeper within 14 days, it is still valid. The registered keeper then has an obligation to identify the driver.
The driver may then receive further paperwork in due course, but that is not to be confused with the document that is legally required to be sent within 14 days.
NIPs can also be issued verbally to the driver at the time of the offence or alternatively, you could receive a court summons through the post for the alleged offence within 14 days.
Small mistakes on the notice do not render it ineffective unless it would mislead the potential defendant.
A Notice shall be deemed to have been served on a person if it was posted to them at their last known address, notwithstanding that the notice was returned as undelivered or was for any other reason not received by them. A posted NIP is deemed to be served until the contrary is shown.