As I was sitting down to start writing in earnest on the third chronicle of Brother Thomas—having worked out the characters, what really happened, etc. to my satisfaction—I looked for the file where I wrote down biographical facts about my main characters. I couldn’t find it. Worse, I have come to conclude that I can’t find it because I never wrote it.
I am not, it should be noted, talking about lengthy backstory in which I wrote out novella-length descriptions of each character’s experiences in kindergarten, grade school, middle school, high school, etc. I’m just talking about the basic facts: height, weight, hair color, birthday, date of joining the order (if appropriate) etc. Having not written these things down when I mentioned them in the previous two books, I now have to comb through the books to see what I in fact did mention. It’s not entirely wasted effort since it’s a good idea to read the books to get the tone of characters fresh in my mind, but at the same time it’s a lot of work that I really wish I didn’t need to do right now.
So, a hard-won lesson, which I pass on to any readers who are just getting started on a series of books: make sure to keep a file open for facts about your characters who will show up in future books. It will save you a ton of effort down the road.