Atlantic Gull

On the weekend of 1-2 may I was in Westman Islands and saw this interesting gull . I managed to shot lot of pictures to confirm the ID . It looked similar to Lesser-black backed Gull but some things didn´t fit so I sent pics to a friend Peter Adriaens a gull specialist I was lucky to meet in SW-Iceland a month earlier . He soon found out it couldn´t be a LBBG and suspected it to be an Azorean subspecies of an Yellow -Legged Gull . He forwarded the pictures to two other birders which had lot of knowledge about the Azorean ssp. They at once confirmed the ID of Larus michahellis ssp.atlantis . I welcome any discussion .