coma or vegetative state?

My  22 yr old nephew was robbed and beaten about 3 weeks ago and has yet to regain consciousness.
Initially his glasgow score was around 9
Around day 11 he began to open his eyes. and vocalize. he looked like he was beginning to emerge, as i understand.
he then had a setback involving pneumonia and oversedation...
For several days now he has again been opening his eyes and today appearing to move his limbs purposefully.
I am at a distance and have no access to him  his drs directly.
My question is, how is the distinction made between someone who is coming up out os a coma and who is in a vegetative state? does it have to do with how long the condition remains the same?
Does everyone coming out of a coma like this pass through a Vegetative state?
The only clear distinction between Coma and VS is sleep/wake cycle. How is this ascertained?
Thank you.

[auntiezazz]

does anyone know the answer to this? I would like to know how they tell the difference between a coma and a vegetative state . I would like to know this so that when I read studies etc. about one or the other I am better able to know what applies to my nephew and what doesn't. He was in a coma, according to the Dr, but at what point would that diagnisis change?
From what I have read, I can not distinguish well between VS and someone greadually emerging from a coma. The clearest marker I have read about is the sleep wake cycle. do the do an eeg to find out if someone sleeps?
Thank you