There is an early buttoholer - "Famous Button Hole Worker" and though they continued to be made into the 50's, the very early ones predate the Singer branded buttonholers (this excludes the Peerless that has "Singer" stamped on it.)
I've seen reference to different attachment types, but have not seen them all so maybe they had a type A or B that attached to the early machines. I've meant to watch and get one of each, but haven't paid much attention to buttonholers for a while.