Anything is possible, but an absence of response to an event that is so outside the normal realm of experience would be unusual. When such a non-response is also experienced within a context of other emotionally dis-regulated responses (whether of anxiety, depression, suicidal impulses, SH), it's more likely to be a defense. You remember the incident, but don't remember it as traumatic--but you also believe it to be your fault. That belief serves a protective purpose, the same as my memory repression/depression served a protective purpose. But ultimately, the cost of all that repression/depression was too high. It's a kind of denial defense.

I also had issues with dissociation in the first couple of years of therapy, probably because I dissociated during incidents of abuse. So those experiences were repressed and were never processed at the time. When they began to surface, all the emotion connected to the experiences surfaced, too. As long as the defenses stayed strong, the memories and their associated emotions, stayed buried. But a lifetime of depression took a toll.