possible Ring-billed Gull (first winter) in Osaka

I was going through my old files of Common Gull images last week trying to make sense of the huge range of kamtschatschensis appearance when I came across this bird. When I originally saw it (13 March 2011) my initial though was Ring-billed, however it didn't look the classic I would hope to find in Japan so there was plenty of room for doubt. To my knowledge there have only been three or four Ringers recorded in Japan, all adults. So perhaps a first of sorts, is it a major rarity for Japan or a further, and far from needed, stretch of the identification parameters of kamtschatschensis?

After resolving it was unlike any kamtschatschensis I'd ever seen but that the brief views I'd had weren't good enough to claim such a rare sighting, I put it on the back burner until re-discovering the images last week. Now I find myself agreeing with my feeling at the time, that it could well be Ring-billed, particularly as Howell and Dunn (Gulls of the Americas) state that the inner primary window and corresponding wedge of greater primary coverts can be dull.

It was on one of the closest sandbars when I picked it up, the long legs, deep body, heavy chest, angular head and thick bill combined to create an arresting jizz. Probably because of the longer legs it frequently adopted a far more upright stance than the Common Gulls. The plumage features here can all be shown by kamtschatschensis though birds with very scaled breast markings usually also have heavier hind neck blotching and the rear ear coverts spot never seems to look as isolated and conspicuous as it does on this gull. Though the saddle is very pale, almost all first winter kamtschatschensis have much paler grey saddles than adults. The primary projection looked deeper than that of Common and had three evenly spaced tips between the tertials and p9. The blade of Common looks narrower creating a longer impression and the tip of p5 often, though not always, falls conspicuously beyond the tertials frequently producing a pattern of four unevenly spaced tips.  

There was barring on the outer feathers proximal of the tail band but nothing sub-terminally.  

Though Ring-billed is supposed to have a contrasting whitish centre to the underwing, the coverts bar on this bird is actually less contrasting than on most kamtschatschensis.

The only shot on water; angular head and heavy bill aside it looks a little odd, flat-backed and low in the water. The tertial fringes appear very narrow but see below. 

It would be strange to see a first winter kamtschatschensis, any age for that matter, with such worn tertials in March. It makes judging how broad the white fringes might have been difficult, but possibly too broad for Ring-billed?

The overall impression in flight was of a broad-winged powerful gull. The primary window and inner greater primary coverts often looked more prominent at distance.

The outer webs of the inner primaries are dusky, not what I'd hope for in Ring-billed but not typical of Common either. The inner webs are surprisingly pale across the outer wing.

The jizz was more of a large white-headed gull rather than Common.

A heavily cropped and sharpened head shot.

Feedback about this gull from a few people mentioned some features, which I was really already aware of, pointing away from Ring-billed but one in particular refering to the median coverts pattern has convinced me this is kamtschatschensis. Albeit, in my opinion, an exceptional one.