Words, as is well known, are the great foes of reality.
Writing a memoir or autobiography for another person, or perhaps even for yourself, presents the well known problem of getting at the fact versus the fiction or invention (the same thing) of what happened in the past. What do you do when the subject of the book only remembers snippets of a conversation or fragments of a scene? What if the subject does not have the descriptive skills to make a significant character in his story come alive with details about that character's appearance or mannerisms? What if his descriptions of place and people are limited to adjectives such as "beautiful" and "nice."Joseph Conrad
One approach would be to leave out everything from the period before my client could remember events clearly, as Stephen King did in his memoir, On Writing. That works for the the first problem but doesn't solve the question of detail. Another is to use a tool that historical fiction writers employ, research.
I decided early on that I was going to rely on research. I had photo albums from as far back as the 20s and a diary from the subject's mother to describe the environment that the subject, and his parents, grew up in and to fill in details about stories handed down from his parents. I used these materials as a jumping off point for further research on the Internet.