For clarification--------------I use the term 9 patch to refer to any pattern that has a 3 main pieces by 3 main pieces pattern. And for 4 patch, any pattern that uses 4 main pieces by 4 main pieces. Each of those pieces may include more than just a couple pieces.
In my files, even the beloved Charpenter's Wheel is listed as a 4 patch, since it can be done as 4 separate patches.