"The Nature of Proof in the Interpretation of Poetry"

I always assumed that in poetry the poet had a specific meaning that was going to be conveyed in a creative way through words. I though it was the readers job to try and find the meaning that the author wanted. But i also though that along the way one would be abel to find their own interpretation of the poem that had possibly struck a chord with the reader in a new way unexpected or anticipated by the author.Then comes a new theory that the reader's point of view on a work of poetry is correct. Perrine states that the reason poets give into this notion of all views on the their poem to be correct is because "no poet...likes to be caught in the predicament of having to explain his own poems." I understand the concept that, yes, an author is entitled to having a single explanation for his poem but isn't poetry a form of art? And if so does that not mean that it will affect the reader in a way that a painting would bring out an emotion or interpretation.
And yet What confuses me when Perrine says " If more that one interpretation satisfactorily accounts for all the details of the poem, the best is that which is most economical, i.e. which relies on the fewest assumptions not grounded in the poem itself." Does that mean in order to have a "correct" interpretation one must have something that includes all of the details? But if one does include all of the details does that make it what the author wanted? I just don't understand the concept that there has to be one correct interpretation. Although I would agree that if someone made something up about the poem and said that this is what the poem meant then i would have to disagree too. I guess my issue with Perrine's concept is that he is putting a limit on creativity and the different meanings one can take from it. Pretty soon we will be only relying on what the author means and where does the creativity come from , from then on? The authors only and the readers are merely the readers with no mind of their own or opinion.