It was my understanding, and I could be wrong, that the Gen 1's were before the MSR-K reticle were available. The gen1s weren't around long. The gen 2s had upgraded glass a little I believe or coatings I think to deal with CA. They both had the knurled knobs like the pic above. The parallax knob also had detents at the different yardages.
The gen 3s had upgraded glass for even more light transmission, lost the detents in the parallax and had the scalloped knobs. I thought these also came with the option for the left side windage knob but maybe that's a gen 4 or 3b?? I have what I consider a gen 2 with the MSR-K and haven't paid all that much attention to the newer ones because I know if I did I would have had to buy another.