A V is not a IV with extra bits added: the IV is a V with bits deleted! The V came out before the IV (by about 18 months), and the reviews at the time quoted AR-A saying that a V was handmade with selected parts, whilst the IV was assembled with off-the-line parts, unselected. So you might get a IV as good as a V, but lacking a VTA screw, VTF dial and damping trough.
A 309 was a IV with a detachable headshell. An M10 was a 309 with a simpler mount.
And that's all you need to know!