Well the point of the New Year's gift is to "reward" people who are still active around the start of the new year. So maybe if they could tell you were still active, they gave it to you anyway. Like if you logged into the IMVU chat client sometime in December, the little thing in the "about me" panel says the last time you logged in, so they could tell you were still around. Last year they didn't have that little thing in the "about me" panel, so I don't think they could tell before, and they had to tell by seeing who checked their messages and put the stocking on their page.
But I dunno, that's just an educated guess about how the whole thing works.