To demonstrate how an individual can give different interpretations to Blake's illustrations at different times and in different circumstances, lets look at Plate 64 of Jerusalem.
In The Illuminated Blake (page 343), Erdman has this to say about the figure at the bottom of plate 64: "At the bottom this scroll of Natural Religion reaches the Rational Power, and the "Indefinite Spectre" Urizen, with fingers on book, checking with his index finger the message of the blots and blurs on the veil. At the top of the page: "The figure blindly writing the scroll, sleeping on it, yet with a sunburst (yellow against pink) of potential halo around her head is evidently Vala..."
In choosing the picture from Plate 64, as the illustration on the cover of The Complete Poetry and Poems of William Blake, Erdman sees the picture in a more personal manner:
"The design on our cover, constructed upon plate 64 of the Mellon copy of Jerusalem, was inspired by our editorial respect for the Committee on Scholarly Editions (CSE). The proofreader at the bottom with knuckles on text represents the five of us who, as required by the Committee "to prevent recontamination of the text," will have been "scrupulously and repeatedly" proofreading during the course of this book's production. Why that left hand held to shield the text from the light shining from the inspired (but nodding) author, with quill on scroll beautifully unfolding to constitute a New Heaven? Our attention must be upon what the author wrote, not upon our vision of his vision, even though we keep watching. That greater liberty is the reader's privilege."
The Complete Poetry and Prose of William Blake, page XXVII
It is a privilege to read the words of Blake as Erdman and his committee provided them the to us. The greater liberty of trying to discern Blake's vision through the text, we pursue as diligently as Erdman pursued his editing. Without the diligent and meticulous work of Erdman and his associstes, Blake's vision would not be so easily available to us.
Here is the Plate 64 image from the Blake Archive, which allows us to view the only color copy of Jerusalem in existence.