San is 3. Mai I'm not sure

. Laminated steel of 3 layers. The two outer layer is normally of tougher and more corrosion resistant steel and the core or middle layer is of harder material. In this case I think the Cold Steel version is of two layers of 420 steel on the outside and with a core of VG-1.
It is said to be an improvement of the old fully VG-1 voyagers that the corrosion resistance is better. In addition it is reputed that the lateral strength of the san mai with VG-1 core is better than a pure VG-1 blade (on the direction if you want to snap the blade). I'm unsure about this one but the corrosion resistance issue is logical.
Another benefit of combination/composite/laminated design is cost saving I have always thought. Kershaw used composite blades where the cutting edge is of more exquisite material to reduce cost and also for aesthetic reasons.
Overall, I like it. Looks cool. And hope it's not too expensive. I'm cutting down on beer and rice (I'm not from the US) just to maintain my steel addiction
PS: I'm not sure but I think the III is because it's the 3rd generation of the San Mai design for Cold Steel.
PSPS: Other notable laminated blades are the Becker necker with SG2 core, Kershaw Ti JYD2 with SG2 core, and Fallknivens VG-10.