Certainly possible. I relied on the Beckey guides for that section (and NWMJ for more recent climbs). Where would you recommend looking for more information on winter climbs between the border and the Fraser River? Or can you provide more information directly?
Even just using those sources you missed an awful lot, Lowell.
Just two examples I noted quickly looking through the list:
North Illusion, northeast buttress, winter ascent (Kay/Zozikyan 1986 or 1987?).
Slesse SE couloir, first ascent, winter 2003, Neufeld/Isbell
Both of those are in the latest red CAG. At first I though you'd skipped them for some criteria I just didn't understand, but now it seems like you just plain missed them.