I posted the same question about my 041 FB a while ago ,#9655351, and had the same problem. The badge can give some idea I'm told i.e the Stihl badge on the FB was used up to 1978ish ? and the Super badge type after that. I found a batch date stamp of 1976 on the inside of the air filter cover, it was indicating the time date etc when the cover was produced and would tie in with model year introduction.