commercial name is the one used in ads, brochures, badges, etc.
We usually do not store full vehicle numbers or licence plate numbers, just codes identifying model/generation, allowing to regroup different model names (like the W-codes of the Mercedes or E-codes of the BMWs), but for some like the Rolls-Royce we store the individual chassis number or licence plate of the car to be able to track them, as they are much less common and tend to be widely known by specialists (especially old models still on the road, or those used in several movies).

For the Lotus, there can be two names then, one more commercial and one more technical.
For the Esprit, Elan, etc. the technical one (chassis) is then the Type.
For the others, we could either always put the Type as chassis code like those mentioned above, or rather use it as model name if it fits better...