It seems the scoring system for the winter league is definitely going to be open to interpretation. But, I should think, that in an objective driven scenario, for which there are several Mike and more missions in Campaign books
, Achieving the goal of the scenario would constitute a Major win in itself. Unless there are multiple objectives captured by both sides, in which case it comes down to who had the most claimed. That would seem straightforward enough to figure out Major/Minor victory. In Force destruction scenarios, it becomes harder to determine the winner as the two opposing forces could be different in size while still fielding the same points. But since it's by squads or teams, 6 squads/teams aside regardless of the actual size of each squad seems, to me, to be a simpler way to count it out. A four squad, or more, difference between squads players lost would, to me, constitute a major victory/loss. A three or two squad difference would constitute a minor victory/loss. A draw is pretty simple.
And Mike, Warlord does encourage players to write scenarios, and even submit them for consideration for future publication. here's the link; https://articles.warlordgames.com/how-to-write-your-own-bolt-action-scenarios/