As mentioned in the licensing instructions, "Starting from the 4800 model and above, each appliance running R75.40VS,R76 includes a total of 2 Virtual Systems (all SW Blades available on the GW are automatically supported on the free VS)"
This might cause a confusion about what is exactly meant by the phrase "Each appliance comes with an initial 2 VS license".
Meaning, VSX GW +1 (initial 2 VSs license only covers VS0 and VS1).
The goal here is that customer run just 1 VS for practice purpose, see if it is something that would fit his environment. If it works, then customer can simply add additional VSX licenses and continue to grow. If it does not fit, then simply roll back to Single Gateway mode on the appliance with no further effort.