Lack of black tip on the bill is not a major problem. Moult is complex, as noted in 'Terns' and Adrians bird might not be fully adult (maybe a 2nd summer ?) due to darker lesser covert bar and a brownish primary covert, but the outer primaries doe´s look blacker than the inner one. According to 'Terns' Saunder´s moult later than Little (variable), and normally retains thre outer primaries which are deeper black comp. to Little. Number of black outer primaries is a variable character, and as Th_SQ mentioned a combination of characters would of course be wise. That head pattern on a 'clean' Saunder´s I would like to see! Intergrades complicates the situation further.
Check headpattern, males and females on Little here (from Northern Europe)
http://home.swipnet.se/~w-48087/faglar/materialmapp/ruggmapp/albifrons.html
JanJ