There is a lot of churning going on in those numbers. A family head is almost guaranteed four hours and four RV for study time. Also, it is not unheard of for pioneers to also study with the children within the congregation - even if the kid is counted as part of the family study.
There is also the churning of magazine placements. I remember way back when that I was able to count a subscription placement when I renewed the subscription for my unbaptized children. Since the subscriptions are no longer in existence I am sure that family heads count as placements four magazines a month for each of their unbaptized children