It has Cadd3 on it, that’s the really easy one. When cannondale added disc mounts they created the Caad4 and the Caad3 was the basic frame for below the F1000 models.
I didn’t know that. Couldn’t that be faked by decals though?
I’m far from a Cannondale expert but always was told to look for the top luggage mount. If it’s not got it , it’s decent.
This frame in question could be identified by the serial number and by using vintage Cannondale site could it not?