Not perceived (6)
(Other definitions for unseen that I've seen before include "Concealed" , "not exercising pupils?" , "Invisable" , "Unobserved" , "not processed by pupils?" .)
(Other definitions for unnoticed that I've seen before include "ignored" , "Continued to be not observed" , "Overlooked" , "not commented upon?" , "Continued to be unseen" .)