Few comments are found in individual species in Compendium of seashells (Abbott 1986) because of its space constraint. However, when it comes to Neptunea cumingi, the author exceptionally made a remark as " A very variable species" Let us explore how variablity it is.

Colours - light to dark

The shoulders -  round to stepped

Sculptures on the shell - from smooth to very produced

Viewed from the tops

Shapes - from slim to broad

More occurence of sinistral  is found comparied to other mollusks.

(Above pictures were taken from my specimens for sale or sold already)

Reference:

Abbott 1986 Compendium of seashells, the species name given by Abbott is Neptunea arthritica(Bernardi,1857) with cumingii Crosse Syn.

Qi Zhongyan 2004  Seashells of China. This book uses Neptunea arthritica(Bernardi,1857) as  species name without referring to cumingii.

Qi Zhongyan and Ma Xiutong 1989 Mollusca in Huanghai and Bohai, Here it is regarded as a subspecies and is named as Neptunea arthritica cumingii Crosee

T.Okutani 2000 Marine seashells in Japan  Neptunea arthritica cumingii(Crosse,1862) , it is named as a subspecies also

D.MIn Mollusks in Korea , named as Neptunea cumingi Crosse,1862