Or is it YLG?

6th February - I saw the 1st winter LWHG again that I'd called as Casp yesterday and had some doubts that it wasn't a Yellow-legged Gull.  It has always been fairly distant, but some of the features don't seem quite right for Casp.  In particular, what looked like a faint shadowy effect from the back of the eye yesterday looked more like a defined eye mask today - a good YLG feature, but not good for Casp.  Also, a slightly better look at the inner scapular markings, showed some lower ones that looked like the double anchor marks of YLG rather than the faint single anchor marks of Casp.  It still shows some features that are good for Casp, but equally a slightly built YLG might show them as well.  In some ways, I should be pleased if it is a YLG, as that would be a year tick, but it is not a great feeling to call the wrong bird initially.  I am hoping to see the bird again in better circumstances to confirm in my own mind one way or the other and have also sent some of the distant record shots to a renowned expert for comment, but I think I know what the answer is.  Gulls, don't you just love 'em!