I have had a Type II for many years (since 1972).
I always thought the serial number was 500446 as that was the number on the base plate. I only recently removed the baseplate, only to find that the serial number on the main assembly was 500447.
I presume that this an assembly error at manufacture, (or may be not?)
but which is the correct serial number to use?

Ha, 500406 says hello. I'd use the lower of the two serial numbers and you might want to check the Curta Registry to see if someone else has the other one. If so you could put things right by exchanging baseplates!

I would send it back to Contina AG . . .



and yes - it happens... I own a 8778 / 6778 Curta Type I mixed number model - I would never change the rare combination