After watching just2good's second video of opening the HP cmf s2, he said they were from the same box (56 in total as 4 were already sold when he got the box), the distribution are as follows;
(x4) Harry Potter, Hermione Granger, Ron Weasley, Luna Lovegood, Griphook, Moaning Myrtle, Professor Pomona Sprout, Neville Longbottom
(x3) Albus Dumbledore, Lily Potter, James Potter, Ginny Weasley, Fred Weasley, George Weasley, Bellatrix Lestrange, Kingsley Shacklebolt
This would confirm we at least get 3 full sets per box.
A normal 16 minifig series (except for disney s2) would have 3 figs (x5), 6 figs (x4) and 7 figs (x3), so my guess for the 4 packs that were missing from his box would mean Harry/Hermione/Ron would be a (x5) and one of the (x3) would become (x4).