I just found out that a MIAM (Mediation Information Assessment Meeting) is only valid for 4 months
https://www.mediateuk.co.uk/ultimate-guide-to-attending-a-miam/#:~:text=A signed C100 or Form,make a new MIAM appointment.
"A signed C100 or Form A is only valid for 4-months from the date of the mediator's signature."
The rest of this guide is really useful
https://www.mediateuk.co.uk/ultimate-guide-to-attending-a-miam/