Just reading source code is a whole different experience than actually implementing something yourself. Implementing something pretty much forces you to "be right" in your understanding, while reading can be anything from "really studying" to skimming.

Completely agree, though sometimes you HAVE to go through existing source when you do something wrong. I've implemented libraries based off of specs and white papers, and even then there's some vagueness that doesn't work in practice when there are holes.

Love to see things like this all the same as they tend to solidify protocols/specifications. This of course can have both good and bad results.

I haven't even looked at the git source code. My implementation was based mostly on the official docs. The docs include a section on the internals: https://git-scm.com/book/en/v1/Git-Internals