All Canon FL and FD lenses are breech lock. How do you suppose they could make the change between the old style with chrome ring and the later type while maintaining complete compatibility? The only difference is in how the breech lock is operated.So for these lenses the choice between new and old is mainly in the comfort of changing lenses. (true bayonet versus breech-lock).
Canon's first bayonet mount for SLRs was the EF for the EOS cameras.