There are no limits at all on what meaning we can project onto a text, but if we're interested in extracting information from a text, limiting our interpretations is necessary. Of course, the information we can extract from a text is not necessarily limited only to things the author consciously put in it, but since the information isn't in the text, it's in the text-in-context, then to the extent that you're independent of the author's context, you're only getting out of it what you put in yourself.

For fictional texts, I'm not sure that extracting information from the text is really the best way of thinking about the text-reader interaction.

The "Wizard of Oz" movie is allegedly very influential in gay culture in America. Assuming this is true, I find it implausible that this was the intent of a movie made in 1939. Does that show that the movie can't "mean" something about gay culture?