There were still plenty of "AG" and "B" brevet wearers around at that time and my first flight commander at Halton actually wore an "O" brevet. Which possibly made him unique at the time....68-70.
Not quite unique, a certain senior officer at nav school 1969-70 still wore this brevet. There were some mutterings that the old description of the 'O' brevet as "the flying a****ole" was particularly appropriate in his case.