A valid memory spontaneously re-entering your mind is different.
The idea of "repressed memories" was that people had hidden memories that they couldn't access, even if they tried. According to the theory, even if someone brought up the past event and tried to remind the person about it, they would be unable to recall it happening because their brain had blocked it out.
The idea was that only intervention by a therapist or some other special event could help the person "unlock" the repressed memories, making them available for remembering again.
What was really happening was that some therapists were leading people into "remembering" things that didn't happen through aggressive prompting and pushing, much like what happens when an aggressive investigator convinces a vulnerable person to falsely confess to something they didn't do.
I wouldn't be surprised if there are inaccessible, partly corrupted memories encoded in the hippocampus. I suspect most of them cannot be prompted by a therapist though, and likely there is no practical way to recover them.
I think it's all a matter of finding a trigger (or reference) to grab the memory. A therapist talking to you almost certainly wouldn't achieve that, but walking down the street and smelling an odd smell might.
I once found a recording of a lab session in high school physics. A day I completely forgot about. A moment that had no bookmarks in my brain.
Other things about that day were surfaced. How my braces felt and the fear I felt about forgetting a textbook.
All real, but unsurfaced until then.
That makes sense considering that human memory is strongly based on associations. Activating nearby memories can bring things back.
If you hear the first tones or words of a song you're much more likely to be able to tell the lyrics that follow compared to being asked to say those lyrics based on the title.
I think it depends on the stage of degradation and whether the network is still connected to something that can interpret it.