They look legitimate to me.
They are a non-profit organization. If you click on Bio's you can see the people that work there. They give a physcial address.
Copyrights has a time limit - somewhere around 75 years I think. This is the 3rd edition of the book... very old and certainly not the most recent (I have the hardcopy of the 4th edition). I suspect the copyright is no longer enforceable based on the age.
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