We're probably only a small percentage of actual GG owners, and we're spread so far geographically that it makes it hard to know whats what and where and all that.
I only jumped onto the Gas Gas in 2010, which is when the learning started. From what I understand since 05 it has just been annual updates refinining the same bike.
I think 07 may have seen a revised subframe.
09 got a new headlight
10 saw changes to the water pump cover and rear brake caliper with slimmer rad shrouds and side panels, and introduction of the B frame.
11 was the same as 10, but changed front fonder and headlight
12 saw some major changes
13 refined on 12 again
14 worked on weight savings
There will be more that I haven't listed but thats about it.
Depending when the bikes were available from the factory, who the importers were at the time, how the economy was, and so on etc probably plays a big part in how many bikes are floating around in your area.