[elblanco]

In language, the "correct" case is the more common case for a given variant of the language. The class "English" is composed of the aggregate sum of many variants of the class (dialects, accents, etc.).

Languages change, what was "correct" a century ago may no longer be correct today.

This means the writer has to understand the variant of the language the reader is using, and target that. If your target audience prefers one over the other, that's the "correct" one.

There is no such animal as "correct English" since the definition of "correct English" is set merely by the most culturally powerful subgroup of users of some variant of the language.