The Goetia is one fifth of a larger compilation, and the other four fifths are rarely read.
Book One, Goetia, is the catalogue of seventy-two spirits with its ritual front matter. Book Two, Theurgia Goetia, treats spirits of the air described as partly good and partly evil, arranged under emperors and kings of the compass points, with a hierarchy of its own that shares no names with Book One. Book Three, Ars Paulina, deals with the spirits of the hours of the day and night and of the degrees of the zodiac, and is attributed in the tradition to an apostolic revelation. Book Four, Ars Almadel, describes twenty chief spirits governing four altitudes covering the three hundred and sixty degrees of the world. Book Five, Ars Notoria, is quite unlike the rest: a collection of prayers and orations for obtaining learning and memory, and much the oldest component, with a manuscript tradition running back to the thirteenth century.
The five do not agree with one another. Their hierarchies are incompatible, their sources are different, and their dates are different. The Ars Notoria is medieval; the Goetia's catalogue descends from a printing of 1665. Book Two draws on Trithemius's Steganographia. The binding element is the attribution to Solomon and the fact that a seventeenth-century compiler bound them together.
That is why the question of a single compiler stays open. Someone assembled the collection, but nothing in it was necessarily written for it, no manuscript names a compiler, and the seams between the parts are visible enough that assembly rather than authorship is the natural reading.