My military trilogy contains three books covering a 25-year time span. While I think my memory is excellent, I want to insure what I remember is accurate and correct. Here is how I do that. My books cover a specific time and initially I create a summary of what I want to cover in my book. I then go into more details and work out each chapter (another outline). Then I start on each chapter.
My research tools are vast, dozens and dozens of books written about everything I will be writing about (as an example a military historian authored a book covering a five-year history of a province I was assigned to, it even had a description of a battle I was involved in). I have decoration citations, my officer efficiency reports, letters, documents, and articles of where I was assigned. Also, letters I wrote home to parents and wife. I have battle maps I used and hundreds of photographs.
Probably the most valuable single resource is the internet. I can access government documents, master’s thesis and doctoral dissertations about battles, organizations, and people I worked with, and dairies and photos by service people who were at the same location I was, at the same time. For example, I have a chapter describing my med evac and the evacuation hospital where I was treated. To verify what I remembered I found on the Internet, journals kept by nurses there when I was a patient along with descriptions of what they did and photos of the hospital, ER, wards, etc. I can locate maps, photos, documents, papers, all related to where I was and what I did. Technical details regarding navy boats used in combat operations or photos of planes flown in are all available
This is how I keep myself honest.