The only Cannondale made with a serial number was the Omega series : SM in 1990 (200 bikes) and 1991, SE in 1991(115 bikes) and DeltaV in 1992 (75 if I remember). Those Omega were never shown in catalogs (except sime pictures for showing clothes..)
The 1 MB seems to be a classic serial bike with no edition number written on the frame.
Here’s the article of Mountain Biking UK vol4 April 1991