I have a boxed set of Canon filters like peterm1 except they are Series VI. I also have Canon yellow and orange Series VI, 34mm VU, 40mm UV, 55mm UV, 72mm UV, and orange and red 58mm. I have a copy of Canon lens literature from about 1958. It lists attachments for all lenses for which they are available as Series Vii except 50/1.8,, 50/2.8, and 100/3.5 are Series VI. As darwinwc said, most Canon hoods took series filters, so it seems logical that most Canon owners bought series filters, not threaded ones.
Just a bit of trivia: The metal rim of my Canon orange 58mm filter is engraved as follows, "CANON LENS 85mm f:1.5". However, it is not a lens (no power}, it is not 85mm, and it is not f:1.5. At least it is Canon. As you've heard before: Don't believe everything you read. This includes GPS navigation systems.