Yes, I'm sure you're correct about the earlier date into service of the type. I was thinking more of the red and white ones I used to instruct on, I think they entered service in 1976.
Blacksheep,
We're probably from the same background. I trained on the Whirlwind 10 then went on to the Wessex 5, before going on to earn a living flying the "more modern" Plastic Pursuit Ship - equipped with steam age engine control systems!