[zoomablemind]

> ... a "good" code base, whatever that may mean: awesome test coverage, good documentation, solid organization, consistent styling/formatting, abundant best practices...

IMO many legacy systems were coded to "good" standard for their time. This reflected the choices of idioms, styles, and robustness criteria.

Properly maintained codebase carries those conventions forward. When it's augmented to present day expectations, it's supposed to be done in non-destructive way possibly. There could be seams but not scars all over.

In my experience, the onus is on the inheritors to try and make and effort to keep the legacy code alive yet consistent.

Alas, those assigned to maintenance are often too junior to recognize the consistency let alone care about it. Thus the codebase degrades into a patchwork of "I've been there" marks.