The v2 (yellow) and V20 (black) main frame and fork are very similar. The boom and chain stay, still in aluminum, was redesigned for the V20 to allow for wider adjustability, and the bottom bracket clamps moved inside of the bb cups rather than clamping around the bb cups. The v2 also came with a heavier two-piece fiber glass seat pan, while the V20 introduced the one--piece, lighter weight carbon fiber seat pan still in use today. I put the updated boom, chain stay, and seat pan on my old v2 a while back, effectively making it a V20.
When the V20 came out, some people were sad at the loss of that muscular looking yellow/silver boom and slider. It was indeed impressive looking, but the newer boom/slider did give the bike far greater adjustability. And the re-worked bb clamps opened up what kind, size, and shape bottom brackets you could use.
The V20c (unpainted prototype) moves to a slightly more aero carbon fiber fork, chain stay, and boom. The frame sports a tapered headtube with press-fit bearing cups instead of a straight 1 1/8 headtube with integrated bearing cups. The geometry is a little more dialed (though the old v2 handled really well too). The V20c also replaces quick releases with thru axles, and the older ISO disc brake tabs with flat mount tabs (the v2 and V20 can take either disc or caliper brakes up front, while the V20c is disc brake only up front).