IMO it doesn't matter when someone thinks they have remembered all along and someone who is just now approaching the possibility, the therapy of self care and slow approach is the same.

From what I gather from your questioning is that you feel unsure that what you are experiencing, or being told you are dealing with, is real or not. Whether PTSD is overdiagnosed or not shouldn't matter to an individual who is experiencing issues that fit with it.

There is dissociative amnesia. It varies from disorder to disorder and from patient to patient---there is no set requirement to achieve or not reach. Part of healing though is when a person doesn't dissociate and is able to handle what life hands them. Each person begins that part of their journey from a different spot...some may already know of trauma that occurred, some may only feel like something is wrong...etc.

Don't fear. If you suffer from any of this, there is therapy and treatment for you. If you get into this treatment and find out it's not this, then you are only wiser and have done no harm to yourself. Let it be okay with you.