In reply to Sean Kelly:
I think it's been referenced elsewhere, but the full article on Winter Rounds by the Bob Graham Club is well worth reading, as it's pretty open in their acknowledgement of the complexity of providing a definite set of dates, because it's not necessarily about dates - it's about what the ground conditions are like.
http://www.bobgrahamclub.org.uk/index.php?page=winter
In the case of the James' Wainwrights, I don't think anyone could possibly argue that what he did was not only in winter conditions in terms of timing, but also winter in terms of what it was like underfoot, because if that title photograph isn't in winter conditions - and if two named storms isn't enough - I don't know what is...