How come the original lg env is vx9900, while the env2 is vx9100, should n't the numbers be going up?

im so confused. And i have another question. Which is the best the vx9800, vx9900 (env) or the (supposed to be going up) vx9100 env2How come the original lg env is vx9900, while the env2 is vx9100, should n't the numbers be going up?
I'm saving up my allowance so I can get a LG VX9100 next week.