another Lesser Black-backed Gull conundrum

one thing I find about watching gulls is that I get more confused! -- the variation in upperpart tone of the Lesser Black-backs here is striking but expected? what I find more odd is the difference in structure between different birds -- here are a few -- it also seems odd that some of the darker birds are the small ones? while there is nothing to suggest fuscus it seems odd that the darker intermedius are small birds or is this usual?
the first (upper shot) is a typical graellsii the bird to the right and back is the same individual seen last week -- shots 2-6 a small bird seen today; shots 8 and 9 another blacker bird and shot 7 another dark bird