This is an interesting question. I'm certainly not a lawyer, but it's not obvious to me whether or not removals of code would be copyrightable. If Dev A writes 1000 lines of code, and Dev B carefully removes 20 specific lines that are unnecessary or introduce bugs, the resulting codebase consists entirely of Dev A's code, but Dev B might justifiably claim to deserve credit for their effort. I'd like someone more familiar with copyright law to chime in.

Here's my understanding. I'm not a lawyer and don't know a lot about copyright or derived works either, but the "creativity" thing comes up in discussions sometimes.

If you give me a sequence of integers from 1 to 1000 (which is not a creative work and therefore not copyrightable), and I selectively delete some of the integers such that the differences between adjacent numbers contains a fun message in ASCII, and publish that sequence, the result is copyright because those particular deletions add a creative element.

But if I just deleted every alternate number in the sequence, that wouldn't be copyrightable because it's not creative. (Although you can imagine some scenario when doing so might be creative, it would need some reason why it was.)

Basically, if Dev B does a change that passes some threshold of creativity, then they have a claim. If they just go through and delete all the blank lines and reformat in a standard way, they probably don't.

In your example, I think it would depend on which 20 lines and whether they were trivial changes to figure out.