First of all, thanks for all the replies, and Yes I have read the posts from Hendie about his 1/48 and the on going battle of Fly 1/32 Wessex, learnt a lots from it.
There are small disc on both side of the lower fuselage, you can see clearly from the Pete's photo above, with black dots (Post #403) but you can found them on both side, so it should not be for Nitesun? I do not know how to post photos here yet, but a quick search from most of the HC2, you will found them if you look carefully. Even the Mk 4 of the Queen's Flight, in Red, but those small black dots, so there must be a purpose of them? Just want to confirm it they are HC2 only as I could not find them on HU5?
Those larger round plates with double rivets are even more mystery, and it seems Fly get them right with number and locations? Not just the HAR2 has them, the HC2 have them too, but this photo show them very cleary?
http://nabe3saviation.web.fc2.com/explanatione-fr.html
My question remained whether those large round plates are HC2/HAR2 only?