In the past , Candidates were not given the opportunity to do a CVW and Summer Seminar. At one point in recent years, the message went out that every Candidate would be offered a CVW, but I think that was backed down with the reality that USNA simply doesn't have that much capacity. Now it is kind of as ALW notes, offered by Admissions based upon unknown criteria. If you want to attend a CVW, I recommending letting your BGO know, and he/she can submit a request. In addition, I would expect a timely submission of application is helpful.
Finally, don't fret if you get an invite and can't make it ...many Candidates don't attend for a variety of reasons, including HS activities, too far, too expensive. If you get invited and can't intend, I would encourage telling your BGO , so he/she can comment on that the fact that your declining a CVW is not an indication of lack of interest.