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.
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.
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.