Interesting point you raise BEags, about retrospective issue of Silver Jamboree gong, or the legality of wearing one "acquired" elsewhere.
ISTR that anyone involved in the parade (of "sleepy Fred" fame) got one, so that accounted for many below sqn ldr (including many tossers who happened to be sqn standard bearers, by sole virtue of being tall, slim and with uniforms that fitted - three strikes against moi there then!).
Biggest problem was that ALL Station and Squadron commanders got them, so of course the average age of recipients was quite high. I think a major factor in the policy was that 1977 was in the middle of the cold war medal famine, where many senior officers had nothing between their wings and their buttons..... and saw a way out ....