Black Brant Challenge

I've spent the last three days looking at the Brent Geese around Foulney and Roa Island after getting an e-mail about a possible Black Brant there . It didn't take me long to realise I know little about Black Brants and even less about juv/1st winter plumage.The Collins field guide and the Advanced Bird ID guide by Van Halen offer hints but not enough for me to say for sure.The original finders pics can be seen here http://www.gobirding.eu/Diary/2012/December.html and http://www.gobirding.eu/Photos/BlackBrant.php
Here are some I took of a bird which caught my eye but truthfully I just can't say

  I could only find 2 1st winter Dark bellied Brents and 6 Pale Bellied.
 Comments welcome and links to references and books/articles especially so.