Need help regarding Cello Duet 350

Hello everyone,
Please, I need some help me regarding Cello Duet 350.
Is there any Mark I, II or III serial number during the production of this amplifier ?
I am the owner of one Cello which serial number is around #500 and would like to purchase another one which is #006.Is there any differences between those two ?
Thanks for your replies and have a great day,
I don't know about the serial numbers, but I can tell you the the earlier Duet 350's had a white power switch in front, and the later ones had a black switch that was slightly wider.  Sorry I can't be of more help.