Yale Digital Content reports that it holds:
William of Ockham, Summa Logicae, etc. General Collection, Beinecke Rare Book and Manuscript Library, Yale University.
Manuscript on paper (thick, coarse, some deckle edges; watermarks indistinguishable) of William of Ockham, Summa logicae. With Walter Burley, De puritate artis logicae tractatus brevior, beginning of text only.
Creator: William, of Ockham, ca. 1285-ca. 1349.
Publication Date: [between 1400 and 1450]
Type: Archives or manuscripts
Physical Description: ff. i + 125 + i: paper ; 222 x 145 (195 x 110) mm.
Note that it is desribed as Written by a single scribe in small, cramped and highly abbreviated gothic cursive, so it is presumably not a "first edition". But given that it apparently predates your date for first publication (1488?), it may be useful.