Original AR8200 had a green case. MkII and MkIII have a black case and revised keypad layout. Not all MKIII examples advertise it on the front - my own doesn't anyway! MII and MKIII can be told apart by their frequency coverage if you can access the radio. Each version has been supplied with different rechargable batteries but as I binned them all I can't remember exactly what changed ...IIRC it was capacity difference with MKII and then change to NiMH for MKIII?
I'm sure an e-mail to AOR would yield the serial number differences and any other easy way to tell them apart.