I will try to tell you what I believe but know full well that does not make it absolute truth.
Where a single major trauma has occurred it is probably true to say that the more complete the re-experiencing, the more complete the healing.
Most childhood pain however is not from a single huge trauma, if we exclude for the moment the trauma of birth.
Most childhood trauma comes from the long slow years of repetitive hurt and loss.
This is covered in Chapter Two of my online book, Help Me - I'm Tired of Feeling Bad.
Most hurt is due to not having one's selfhood honored through lack of empathy, love, and touch and bad parenting practices carried forward across one's whole growing period.
Where these multiple small traumas continue for years, then slowly but inexorably, tension such as grief and emotional pain of all sorts start to build, each thing adding to the next until very large amounts of unexpressed "pain" come to be contained within the mind and body.
I do not believe that every trauma must be experienced. What must happen, however, is that in many people this "pool" of pain must be drained with an amount of accessing that comes close to equaling the amount of pain that was brought into existence, and the time required to create it. That is why primal therapy can take years. It is also true that the brain is quite capable of containing a great deal of unprimalled pain without destabilizing. So not everything must be emptied in every instance for return to reasonable health. This is a very individual problem, leading to certain trade-offs where pain still exists.
When a primal person succeeds in reliving a significant event in their childhood, then a tunnel of access is opened, which will allow, further relivings of more and more of these events and or more and more of the depth and quality of these and similar experiences.
Every single event, therefore, does not have to be relived to desolve the core of the problem and return the central nervous system to reasonable calm.
We may return over and over again to a representative incident, or series of incidents, across a number of years of primaling. The tunnel is opened and the pool is being drained.
Completeness of experiencing any given event is very helpful, but that kind of explicitness is not needed with each primal in order to return to health. As one primals over a number of years more and more tension will be released and more and more may be seen and felt with greater accuracy, but I wouldn't turn super accurate complete sensory reliving into a fetish.
Now, the depth of the trauma enters into this problem. Where the hurt has been profound, a great deal of reliving may be required. In addition to this where the parenting has been poor, again, a great deal of reparative work must also occur.
For instance, in a long and difficult birth, so much harm to the individual may be done during that one event, that later people may find themselves reliving that trauma over and over again for years. I personally have the fear that they may get trapped in an endless circle of reliving. There are articles on the Primal Psychotherapy Page that deal with this and John Speyrer, is himself a far better resource than I am in this particular issue.
I have strong beliefs that the reparenting effect of the therapy is very, very important in helping these wounds to close. It is not just enough to reconnect with the wasteland of childhood. I believe that a strong and healthy bond with the therapist is needed to help rebuild the container of the mind/body axis.
Touch and holding may be necessary, and again they are described in detail in my book.
If you do not have a computer to access my book, send twenty five dollars U.S. to me, Dr. Paul Vereshack at Paul Vereshack, 2060 Queen Street East PO Box 51556, Toronto, Ontario M4E1C0 Canada and I will mail you a copy. You will find that it answers almost any question you have, in 180 pages, in very simple language.
I came to primal therapy after I read The Primal Scream by Janov in the early seventies and then by incredible good fortune, my best friend, a woman psychiatrist spent a year with him in California and came back to Toronto. I entered her classical primal practice as a client for four years and my journey began.
After you have read the book, please feel free to communicate with me.