&gt; This seems a bit counter-intuitive given that serious problems are still being found years or even decades later. Perhaps battle-tested is insufficient.<p>Bugs will always exist.  But that statement will apply equally to any software, regardless of language.<p>&gt; New code can take advantage of the battle-tested nature of the original code even if it&#x27;s in a different language.<p>That&#x27;s why I referenced the Peter Naur paper on Programming as Theory Building---in practice, that may very well not be the case.