Not able to contribute much and nothing to this gentleman's question, but how many flying Wessex are there? I don't suppose there are very many, it being quite a large, complex, military helicopter.
Having said that, in my 'other job' as a Scout Leader, we were at Downe camp (Downe Scout Activity Centre) on the weekend 22nd - 23rd March, which is immediately east of Biggin Hill airport (aerodrome?). During Sunday morning session, outside building major projects, there came the sound of something rotary winged and, to my ear, rather unusual.
Seconds later a Wessex, in grey with, I think, 'RESCUE' about its person flew low in towards the airport. Having not seen a Wessex - I've heard them called the Paraffin Parrot I believe? - for many years and the last time in Florida at least five or six years ago, I was surprised and pleased at this minor 'plane spotting coup'.
Just thought it was at least partly relevant.
Roger