The very simple answer is that they do not differ, and have not differed for a very long time (i.e. 20+ years). As documented in the “Creating a Change Package” section of the User’s Guide (the 8.3 version of which can currently be found here):

“...There are no processing difference [sic] between super and complex change packages...”

Both terms have been retained simply to ensure that customers can stick to the name with which they are comfortable. Technically they are identical.