A fantastic article on the 'Identification of Fea's, Desertas and Zino's Petrels at Sea' by Hadoram Shrihai, Vincent Bretagnolle and Francis Zino appears in this month's Birding World.
It contains an amazing series of photos of all three forms/species, a discussion of field characters plus a statistical analysis using a system of scoring various plumage/structural features. It contains a wealth of information and provides great help for at-sea identification.
Further, it also provides a summary of features for Soft-plumaged Petrel, again with some great photos. It lists a restricted white inner underwing covert patch, usually just 'the leading and smaller lesser coverts and a few axillaries; otherwise quite a dark underwing; a restricted white throat patch; often the rump and uppertai; coverts are concolorous with the mantle, with the tail quite dark - including the outer tail feathers. My question would be, how do the images in the article and the features listed compare with the bird identified as Soft-plumaged Petrel in Norway?