If you could modularize code in such a way the sizable chunks could “just sit still!” then entire modules could be marked as perfect. But you wouldn’t have to since you wouldn’t naturally need to touch them (e.g. how many codebases are using a fork of core-utils, for example, … to exaggerate a conways law effect).

But unfortunately the modules don’t make themselves apparent at the start of the project. So it needs refactoring discipline.