Git's built-in diff algorithm is particularly bad for text. Since it's aimed at line-oriented code, it does line-based diffs, which is horrible for ASCII text that is reflowed, because every line in a paragraph will show up as changed for a small change.

Example: https://github.com/divegeek/uscode/commit/1fb2d83137dad1c6ca...

What's happened is that "Section 2" was moved later in the sentence, abbreviated as "Sec. 2", "of" was deleted, and "act" was capitalized:

    Section 2 of act July 30, 1947, ch. 392, 61 Stat. 674, provided...

    Act July 30, 1947, ch. 392, Sec. 2, 61 Stat. 674, provided...

The rest of the paragraph is unchanged, but git shows a 6-line diff with the entire paragraph replaced. GitHub attempts to do some word-based highlighting (see the timestamp lines), but it falls down on most of these paragraphs. Wikipedia's diffing tends to work better for this kind of thing; I'm not sure what they use. The upshot is that the number of lines changed may be a 5-10x overestimate.

I did some work & research about diffs when I tried to visualise progression of slovak law. My best attempt was a diff method that would understand the inner structure of the law. I ended up with simple draft but I am sure somebody more competent could look into that.