I have a Cannondale Carbon Synapse 2 in my possession. Donated to our local bike coop from the original owner who bought it from a reputable dealer. I could not find a serial number on it anywhere. There is a sticker on the bb that looks more like a date of manufacture code. I often look up expensive donations at Bike Index and this number came back as stolen but as a different model. I suspect another Cannondale owner entered that same dom/part number as their serial number. I guess you looked up the dom/part number and got a hit due to Cannondale owners not knowing what their bikes real serial number is.
I asked about this "serial number" at vintage cannondale but got no reply. I think it's just too new for them.
IMO, a sticker is not a responsible way of putting a serial number on a bike frame. I've seen many bikes with bar codes and numbers on a sticker but they all had a legitimately stamped serial number in the metal that matched.