666 is technically correct in respect of your narrow question, completely ignoring the context. In much the same way that a chocolate teapot can be used to make tea as long as the water is cold.
The 6 months time limit is for instigating court proceedings, not for you to receive the SJPN, appear in court, or any other event which does not consist of issuing the Written Charge and SJPN.
They cannot lawfully instigate proceedings within the 28 day suspended enforcement period of the COFP, so any COFP issued from just after 5 months would be a get out of jail free card (assuming that you do not accept their COFP).
Back in the days of hypothecation (when the police received the fixed penalties and deducted their "operating expenses" before passing whatever wasn't left to the treasury), the police would often issue COFPs too late to prosecute if they were not accepted. Since that stopped (to be replaced by taking a £35+ cut from every speed awareness course they manage to sell), such incompetence has been quite rare.
BTW, since when is 04/12/2024 not 6 months after 04/06/2024, but a day shy?