That's it, every line of code is an implicit requirement, based on explicit requirements; when you have a codebase that needs to be maintained or replaced, as a developer it's your job to determine which of the implicit requirements in code are explicit requirements for what the application does.
I do think that in a few years time, next generation coding LLMs will read current-generation LLM generated code to improve on it. The question is whether they're smart enough to ignore the implicit requirements in the code if they aren't necessary for the explicit ones.
(this comment makes sense in my head)
Most if not all of my professional projects have been replacing existing software. In theory, they're like-for-like, feature-for-feature rewrites. In practice, there's an MVP of must-have features which usually is only a fraction of the features (implicit or explicit) of the application it replaced, with the rewrite being used as an opportunity to re-assess what is actually needed, what is bloat over time, and of course to do a redesign and re-architecture of the application.
That is, rewriting software was an exercise in extracting explicit features from an application.