The form Walker, Leslie John is found only in Polgár, citing an entry (not seen by VJTL) in Encicopedia filosofica, and is assumed to be an error--VJTL.
BL Web OPAC, May 13, 2003 (hdg.: Walker, Leslie J. (Leslie Joseph); Walker, Leslie Joseph; usage: Leslie J. Walker, Leslie Walker)
LC database, 6 May 2003 (Walker, Leslie Joseph, 1877-)
LC database, May 13, 2003 (hdg.: Walker, Leslie Joseph, Walker, Leslie Joseph, 1877-; usage: Leslie J. Walker)
Polgár, L. Bibliographie sur histoire de la Compagnie de Jésus, 1981-1990 v. 3/3 p. 673 (Walker, Leslie John [sic] 1877-1958)
Theories of knowledge, 1910 t.p. (Leslie J. Walker, S.J., M.A., sometime Professor of Philosophy at Stonyhurst College)
World biog. index, May 13, 2003 (Walker, Leslie Joseph Ignatius; 1877-1958)