In absence of memory of the original traumatic event, how would the ptsd person discover the initial event?

Probably from eye wi: When there is retrograde amnesia, the only way to get "that which is lost" from one's memory iis to d/w an eye witness.

See below...: Fortunately, healing is still possible even in the absence of the memory of the trauma. Various therapy techniques and approaches can bypass that. While the presence of a trauma is a diagnostic requirement for ptsd, a detailed memory of it, while helpful therapeutically, is not essential... Wishing you well!

Recall: Great question. This is where the dangers of recovering repressed memories enters. Many are open to the power of suggestion, especially when in a vulnerable & regressed state. Thus, it is always important that the therapist not guess at or try to introduce possible past events. The human mind will unfold past memories when it is able to. This is to be respected & should be treated gently.

EMDR: Sometimes certain therapy techniques over the years have been used. Jean-martin-charcot used hypnosis. S. Freud later on continued this work only to find it not very effective. However it did open the door for the birth of psychoanalysis. Today a technique called emdr [eye movement desensitization and reprocessing.] has gotten some notoriety.