Actually, it is possible. As when you have a Destiny Knot equipped to one of the parents, it chooses 5 of the IVs from either parent at random. (Not 6 as people often misbelieve.) This means one of the IVs could end up being the one that isn't 31. On top of that, the last one is random. (Anywhere from 0 to 31.) With the combination you are proposing, there is a chance you will get a 4 IV child.
This happens to many breeders who go for 6 IVs, myself included.