That was my takeaway as well. The weird thing is: since it's someone else doing the initial publication, their omission of copyright credits is costing the artist their copyright. That's... unexpected. I don't know how things worked back then in book art, but if the artist wasn't contracted as work-for-hire, protecting their copyright ought to become the burden of those who actually made the art public. I don't know if this argument was put forth in appeals, but ruling+motivation on this point from the appeals committees are absent from the story.

Sounds like you could accidentally make someone else's art public domain by forgetting to include them on the copyright page...

edit well, perhaps that's part of the reason the copyright laws were updated.