In a well-balanced deer herd, 95% of conceptions occur within a 6-week window. However, that still leaves 5%. A few of those 5% are very early, such as October breedings. But the majority are very late (January and February for an area with a November peak breeding). Most of the time, these are female fawns that finally reach the body weight necessary to enter estrus. But there are always those does with a genetic estrus timing that is very late. Nature gets around to trying everything.