David Clines, “New Directions in Pooh Studies: Überlieferungs- und Religionsgeschichtliche Studien zum Pu-Buch”:

There is little need, at the present stage of scholarship, to attempt a justification of the principle that the dogma of unitary authorship for works of literature must be totally abandoned. In all confidence we may say that a priori we may expect the Pooh corpus (viz. Winnie-the-Pooh, hereafter abbreviated W, containing traditions of higher antiquity than the Deutero-Pooh book, The House at Pooh Corner, hereafter abbreviated H) to be of composite origin; even if there were such a person as A.A. Milne, traditionally the ‘author’, we may be sure that he did not write the Pooh books. His name does not occur once within the narratives themselves, and we can hardly be expected to take a title-page, manifestly a later addition, seriously.