Terms used are im[portant per the IHSAA Bylaws. To clarify, the 12 practice limit is for use of helmets and shoulder pads, known as competition days, (As you said, 5 of those involving teams competing against each other)Every sport has a limit on the number of competition days they can have. Football is unique because of the helmets and shoulder pads and the contact.
That said, football CAN have additional days to work as long as they are not in helmets and shoulder pads.