How Accurate is the Movie, "The Vow"?

I have not seen the movie but from what I have heard and what you described, the situation certainly sounds unusual. Based on your description it seems that the woman in the movie had a dense retrograde amnesia (a loss of access to events that occurred, or information that was learned, before the injury) but was able to consolidate memory moving forward. She did not have anterograde amnesia (a loss of the ability to create new memories after the injury).

There have been rare cases reported of organically based dense retrograde amnesia where the individual cannot remember people in their lives before the injury or even autobiographical information; however, in practice most of these cases, based on both the scientific literature and my experience, are either psychogenic (originating in the mind) amnesias or malingered amnesias.

I think that in many cases, clinicians do not make a distinction in the types of amnesia following TBI.Consequently,, some of these patients will be treated for a neurogenic (originating in the body’s nerve tissue), condition when they may not have one and in some cases their condition will be labeled as psychogenic, when in fact, the disorder is neurogenic; however, as I mentioned, this latter scenario is rare.

The fact that the character in the movie who was injured was able to go back to law school and consolidate memory moving forward clearly suggests that she had an isolated retrograde type of amnesia. If you're interested in reading further about isolated retrograde amnesia, I would recommend an article on the topic written by Dr. Fast and Dr. Fujiwara that was published in 2001 in Neurocase (Fast K, Fujiwara E: Isolated Retrograde Amnesia. Neurocase. 7:269-282, 2001).