Right, and a very good work it is (not an easy task I can promise you),not to mention all the first class images of 2cy heuglini from Russia and the presumed ones from Finland by Visa Rauste. Also images of LBBG graellsii, intermedius and nom.fuscus are first class and very instructive.
Also one has to acknowledge the effort put in to the work on colour ringing schemes for LBBG by all the people working with this project.
Identification of out of range heuglini is a challenge, and will still be for years to come.
Take a look at this site and learn, and notice the similarities between some of the Heuglin´s and Caspian Gull.