Are you proposing a new system be added to the game where we can see how many times we have defeated a certain enemy and how many times they defeated us?
I like this idea. Maybe this book could not only include defeated enemy statistics, but also miscellaneous statistics like distance walked/traveled on a mount, how many times you've used spells you know, how many times fizzled (or a percentage for your hit rate based on how many times you've hit vs fizzled), how many times you've fled battle, favorite spell (the one you've used the most)... All kinds of stats that would be interesting to see!