This is one of those cases where there are two or more hostas with the same name. Neither are currently registered with The American Hosta Society. The first one to be registered would become the "official" hosta of that name and the others would have to be renamed.

According to The Hostapedia by Mark Zilis (2009), "The registered name of this sport of 'September Sun' is 'Clifford's Polar Moon' but it has been marketed simply as the cultivar, 'Polar Moon'.

Hosta Helper will call this plant 'Polar Moon' (Hostapedia)

According to The New Encyclopedia of Hostas by Diana Grenfell and Michael Shadrack (2009), states that H. 'Polar Moon' is a sport of H. 'August Moon'. (But, Zilis says otherwise)

Hosta Helper will call this plant 'Polar Moon' (New Encyclopedia of Hostas)

According to The Hostapedia by Mark Zilis (2009), "...More correctly, it should be used as a trade name, i.e. H. POLAR MOON."

Hosta Helper will call this plant POLAR MOON.