It has "(c) 1991 by Commodore-Electronics, Ltd." printed on the inside of the 3rd editions I have right here.
This is not the last word on the matter. Commodore made contracts with the publishers (Addison-Wesley, which are now part of Pearson Education, and Bantam books, which are now a part of Bertelsmann) which gave them a whole bunch of rights. For example, there were plans for and even early drafts of a dos.library chapter which would have appeared in the 3rd edition RKM Libs, but Bantam books prevailed and had Commodore restrict the DOS documentation to the AmigaDOS manual.
From what I know, Commodore got the short end of the stick with these contracts. By now nobody really knows who owns what. As I hinted above, the original publishers went through several mergers and acquisitions, so you'd have a hard time even finding somebody at these corporations who would know how things stand.
As with so many things in the Amiga market the only approach to settle the accounts would be to claim ownership and wait for somebody to sue