Green-winged Teal, more or less?

question when is a Green-winged Teal 100% ? This drake turned up at Alkborough last year on April 25th and stayed to May 4th, it returned this spring on April 24th and was still there today; between years its white vertical stripe has become broader and better defined and the fore breast looks more intense in colour; It was observed for long periods in 2014 and although never as close this spring it has been watched well with scopes; up until today no-one has mentioned anything untoward about its appearance in deed I was able to get some record shots of it this morning and never saw anything unusual in its plumage; the head has a faint buff line only below the eye and ear coverts, the white vertical stripe looks clear and obvious, the breast is a lovely rich pink tinged colour and there is no horizontal white scapular line  -- or is there?? When it was swimming this morning and feeding I never saw anything on its scapulars there than the usual thin black horizontal line but later on it went to sleep on a mud bank out of the water and above the black line was a clear white line; not as broad or obvious at Eurasian Teal but a white line -- looking at other images of Green-winged Teal from the states on tinternet though seems to reveal that a thin white line above the black scapular line is not all that rare although it clearly does not show up very often? So the obvious question is, can this bird be a pure Green-winged Teal or is it a hybrid? when seen 95% of the time it looks like a Green-winged Teal but is that good enough? When it was sat out of the water it was about 800m away so no images but these are of it earlier in the day and the two bird theory has been rebuked. It also has good rust coloured inner greater coverts a feature sometimes mentioned for non drake Green-winged Teal

Distinguishing Green-winged and Common Teal - Sibley ...

The thorny problem of GREEN-WINGED TEAL identification