Thermodynamic Properties of Steam: Including Data for the Liquid and Solid Phases, Joseph H. Keenan and Frederick G. Keys, First Edition, Thirty-First printing, New York, John Wiley & Sons, Inc., ©1936.

I'll agree with "not previously seen in nature" - - maybe, but properties of supercritical and triple-point water have been quite well known for some time, and have had industrial uses for about a century.

John