Yup, you're right! There were no 64 1/2 Fastbacks. I always do that because I saw a 65 Fastback once when I was young, which the owner claimed was a 64 1/2 and it even had the cooling louvers for the battery. But I later learned that owner must have done that to screw with people. Well I guess his plan worked because it's screwed me up for years now even though I know the truth....No 64 1/2 Fastbacks!
Edit: I'd guess 66 as well because of the back up lights (even though it's an easy mod).