[haimez]

I think declaration vs use Sue distinction is much more helpful to reason about in this context, and named tuples are a classic example of “if you didn’t declare these tuples to be compatible at definition time, it’s probably a bug to let you pass them around as if they were”

[yarg]

Codesmell sure - and a case for refactoring, but I wouldn't go as far as to say bug.

But I wouldn't expect that to be the common use case - I'd generally expect that the caller would just be implicitly importing and using the type effectively declared in the method header.