Histories are for reading, not for storing of data. Second, I said to compile a list of interviewees. After more experience I add, sure, make a list, and sure, prune it according to reliability and importance of sources. But don't wait for the perfect list before you start to ask questions. One interview leads to another, and if you put off this or that person too long, he or she may never be available.
People die, or move away.
Get to the person early and push and pull to get a feel for things. Then check out what you heard. What's written endures, what's said flies away. In this case, what's said flies into the blue yonder of people's recollections, hazy and otherwise. Check what you hear in the interview with what's been written.