Even if someone were crazy enough to use reflection to get around accessibility for testing (which you should never do), once I saw that once, I would be judicious about using “Find all references for a class” - something else you can’t do reliably with dynamic languages.

As far as partial build systems, with at least C# that would still be caught when you do an integration build. But that still begs the question, why wouldn’t you use a proper internal package repo and proper versioning?