I'm sure most people have a few legitimate clear memories (the single one I have is indeed of a traumatic, though amusing, event) of the 4-6 age range, and of course you have your savants; it's the unusual number of people who claim to vividly recall their youth pre-3 to 4 years of age who I'm skeptical of.
A 20 year old real memory is not a recording that you have carefully preserved. It is more like a a clarisworks document on a floppy disk that you copied to a wordperfect doc on a hard drive, then to a word doc on a CD, then to Google docs, and each time you copy it you have any to reconstruct some lost details.
Rehearing and retelling the memory is critical. As such, the actual different in constructing a real memory vs false memory diminishes to kill over time.
She also thought she remembered him saying 3 years old, so 4-6yo memories are perfectly feasible, and I think most people have them. I have loads.