Langsett Caspian Gull

Guilty of the cardinal sin of not taking the sketchbook out with me at Langsett last night, I had to commit the most important features to memory and get something down on paper as soon as I got in!
Not good, but I hope these drawings convey something of the bird and how striking it appeared. For me, all the boxes are ticked bar the primary pattern(s). Is P10 critical? There was definitely something resembling a 'white tongue' on P10, but it was difficult to be certain in the failing light. Also, after looking at pics on Birdguides of the recent Northumberland bird it shows what I assume is wear on the greater coverts. Would anyone know if this is a particular feature consistent with Caspian Gull at this time of year or is just another 'gull' variation?
I'm sticking my neck above the parapet with this as conditions weren't ideal. Hopefully it'll return and not metamorphose into a strange Yellow-legged!

Any comments are most welcome
Cheers
Russ