I have a 1985 Cannondale ST 400. While checking the serial number, the first two letters are BB, indicating a 1984 model. Did Cannondale use leftover frames from one year to the next? I bought the bike new from a LBS near me.
Yes I believe so. If the frames were not sold it is normal for them to use them the next year. If you look at their catalogs during the years you will notice that older frames were used on entry level models while the top models got the new frames. I have owned a F400 model using the same caad3 frame as a F2000 model had 1 or 2 years before.