When a question has been incorrectly marked as a duplicate of another question, is editing that question with a note explaining why it is not a duplicate a valid reason to edit a question. Recently I suggested an edit to a question in such a manner and it was rejected.
It was clear from the comments and title and the question itself that only a small aspect of the question was addressed in another question, but the main question was indeed original. A user reading a question that has a duplicate flag at the top will be misled.
Is putting a note below that tag explaining why it is wrong, a valid next step after making a comment, or should one go immediately to that site's meta go get support from the community? Or should the question be flagged. What is the proper protocol for dealing with non duplicates that have been marked as a duplicate -- if you are not question's author?
For example, a question on SO, which asks mostly about adding a variable value to a plot in R, is being marked as a duplicate of adding an 'expression' to a plot (just because expression is mentioned in the title). At no point in the proposed thread is variable values even mentioned. The OP posted a comment clearly explaining the difference and yet editors continued to mark it as a duplicate, without even responding.
So my good faith solution was to suggest an edit to the question with a note explaining why it wasn't a duplicate, which was strangely rejected for "changing the meaning of the question", despite the meaning clearly not being changed at all (All I did was add "There is an answer to question X: it does not address this question because of Y", where Y is both in the OP's title and in the body and explained by the OP in a comment).
So my question is, are edits explaining duplicates reasonable edits if they are not done by the OP?