London's juvenile Yellow-legged Gulls - do a lot of them actually winter here?

Been seeing a lot of gulls since the last post and will try to catch up on them - a trip to Portugal produced over 60 different rings, two American Herring Gulls, a Caspian and a Glaucous Gull while within 3 miles of my Central London home Caspian Gulls have been rather regular which has been pleasant enough.

But that isn't what this post is all about. It is about Yellow-legged Gulls. London has long been known to get a summer influx of juveniles - from early to mid July peaking in mid to late August usually. They then by mid to late September be much less numerous, and assumed to have headed off to pastures new. Think that's kind of what I write every year for the London Bird Report anyway. But this year has made me re-think things as having two 'distinctive' individuals has allowed a bit of tracking: -

'Swiss Tony' (yellow HD232)
First seen on 31st August and 1st September at the O2 by Jamie P and I, and then Dante and I saw a Yellow-legged Gull at Lyle Park on 2nd January which had a yellow ring. And then Dante saw it well at the O2 a couple of days ago on 4th January with photos here.

Yellow-legged Gull O2 Greenwich, London 1st September 2016

'Pinky'
I first saw this bird on 17th August 2016 on the foreshore by the O2 at Greenwich, and Jamie P saw it either that same day or the day after.

Yellow-legged Gull  O2 Greenwich, London 17th August 2016

It was seen the next week and then has been seen sporadically either near the O2 or east of there at Thames Barrier Park as recently as 23rd December 2016.

Yellow-legged Gull Thames Barrier Park, London 23rd December 2016

So to conclude, or at least wrap this up: -
1. Yellow-legged Gulls that come to London mid to late summer actually winter in larger numbers than previously thought (and in 1st-winter plumage get drowned out by other similar large gulls due to their subtlety) or
2. The two 'distinctive' birds talked about above are perhaps just exceptions rather than the norm and it is just coincidence they've both overwintered

Up to you which of the above you think is most likely, but get a decent gathering of large gulls on the Thames east of Central London midwinter and I'd be pretty sure you'd find a Yellow-legged Gull in among them after a bit of searching.