In North America a "winter ascent" is made in calendar winter only. Even if the conditions are summery, like when Wayne and Lane climbed Yak Check.
In Scotland a "winter ascent" is any ascent made under "winter conditions" - below freezing, snow covering the rock and turf frozen. Even if it's made in October or May. Conversely many North American winter climbs would not be counted as winter ascents in scotland - especially anything where you are drytooling on bare rock as opposed to hoarfrosted or snowcovered rock, even if it's -20C outside.
The claim of December 1 to February 28 is bullshit.