@Morris: I really want some pay off from the ruby. It was instrumental in
Chances and mentioned in CD. It's too powerful to just shelve. I know Jim often sets these things aside for several books, but (whiny voice) I want it now.
A couple of subtler things:
Mab's magical workout training preceding Cold Days. Harry gets better physically but also magically learns to not needs his foci as much.
...
He occasionally invents or uses something new like the electrical chain...
Also something intangible over the series is how scary he becomes to his enemies. He isn't really very scary to anyone in book 1. But now he is really something to worry about, a destroyer of nations and demigods. That impression, that reputation is a very real weapon in his arsenal and armour against his foes.
That's a good point. It's hard to quantify his increase in control. It's obvious and larger in CD, but it also happens in every book. If I was to quantify it by, for example, saying Harry gets plus 1 control in a typical book and plus 3 in CD, I know I'd be wrong, and I'd know people would miss the point and argue that not only was I most definitely wrong, but some different number is clearly and obviously right. In fact, I half expect it to happen based on that sentence.
I didn't even try to put in new foci that only show up in one book or were already present in SF. I pretty much ignored everything that happened and was resolved in one book like Harry losing fire magic in SmF. I'm sure all that stuff would affect his "character sheet," by making him better at handling those situations and crafting items in the future, but it's extremely hard to quantify.
Changes, plus 10 to Reputation.
@Wolfeyes: I would distinguish between knowledge and experience using knowledge. Harry has knowledge or gains it, then he must learn how to use it. He normally learns to use it through experience.