Given that ...AIT/FIT does not have an official CPD - Carnet De Passade En Douane - issuing organization in the country... Should not the question be...Will Cambodia accept and honour a CDP issued by another CDP issuing country/authority on arrival in your vehicle at a Cambodian International Border Crossing?

I don't know but the question is worth asking.

OML

On overlandingassociation.org it says the following about Cambodia:

"Recently travellers entering Cambodia have been asked for either a permit (issued Phnom Penh, can take up to 7 days) or a Carnet to enter the country with their vehicle. A Carnet is not officially required for entry into Cambodia, and the requirement of a permit is something new. There has been little officially published about either of these requirements and it does not appear that these rules are being applied consistently on all borders. Travellers have reported that you may be able to obtain the permit in advance from a Cambodian embassy in e.g. Bangkok. "

This information is dated 2018 so not really up-to-date but perhaps the latest available. According to this website there are new regulations in Thailand since 2016 requiring a guide to travel with the car. Also in Burma. Who knows if the same rules will come back when the hysteria is over.