You figured it out, Royson.
Aircraft registered prior to January 1, 1974 were identified with the Nationality mark CF, followed by three letters for the registration mark.
At one time all civil aircraft were CF-something, then the country indicator became just the C followed by the dash. Now certificated civil aircraft are either CF or CG, with ultralight being CI. Since my bird was brought into Canada as CF-YIL that's how I tend to think of her.
Reinforcing that, in radio calls, we begin with the five-character ident, but usually drop to the last three if the tower does that first. Works, unless your other-letter counterpart is around. I've never run into mine, C-GYIL is a 172M based in Watrous, Saskatchewan.
