London Ed claims that
1. Sherlock Holmes is a purely fictional character
2. Someone made up a story about a person called ‘Sherlock Holmes.'
I don't think this is right. Even if (1) and (2) are intersubstitutable salva veritate in all actual and possible contexts, they are not intersubstitutable salva significatione. They are not intersubstitutable in such a manner as to preserve meaning or sense. (1) and (2) don't have the same meaning.
First of all, it is not in dispute that Sherlock Holmes is a purely fictional person, unlike, say, the 19th century American chess prodigy, Paul Morphy, who is the main character in Francis Parkinson Keyes' historical novel, The Chess Players. (Available from Amazon.com for only a penny! The perfect Christmas gift from and to impecunious chess players.) A fictional object need not be a nonexistent object: Morphy is a fictional object inasmuch as he figures in the novel just mentioned, but he existed. Holmes never existed and never will. Hence the need to distinguish between the purely fictional and the fictional, and the fictional and the nonexistent.
Now let us assume that some fom of 'creationism' or 'artifactualism' is true: purely fictional objects are the mental creations of finite minds, human or not. They are literally made up, thought up, excogitated, invented not discovered. They are literally ficta (from L. fingere). On this approach, internally logically consistent ficta cannot be reduced to real, albeit mere, possibilia. For the merely possible belongs to the real, and cannot be made up; the purely fictional, however, is unreal and made-up.
Let us further assume that artifactualism about purely fictional items, if true, is true of metaphysical necessity. It will then be the case that (1) and (2) will be either both true or both false across all possible worlds. But they don't have the same meaning since one who understands (1) may easily reject (2) by holding some other theory of fictional objects, say, a Meinongian theory according to which Sherlock Holmes and his colleagues are mind-independent nonentities.
London Ed is making the following mistake. He thinks that 'x is mind-made' follows analytically from 'x is purely fictional' in the way that (to introduce a brand-new example) 'x is male' follows analytically from 'x is a bachelor.' 'Tom is a bachelor' and 'Tom is an umarried adult male' have the same meaning; the latter merely unpacks or makes explicit the meaning of the former. But (2) does not unpack the meaning of (1): it goes beyond it. It adds the controversial idea that purely fictional objects have no status whatsoever apart from the mental activities of novelists and other artistically creative persons.
Ed may be misled by the etymology of 'fictional.' Pace Heidegger, etymology is no sure guide to philosophical insight.
If you say that Tom is a bachelor but not an unmarried adult male, then you contradict yourself, not formally, but materially. But if you affirm both (1) and the negation of (2), then you involve yourself in no sort of contradiction. Some maintain that purely fictional objects are mind-created abstract objects. People who hold this do not violate the meaning of (1).