I fear you're overthinking things.
Originally posted by MTR 7.4 Abnormal Product:
Neither Wizards of the Coast nor the Tournament Organizer guarantee any specific distribution of card rarities or frequency in a particular booster pack or tournament pack. If a player receives an unconventional distribution of rarities or frequencies in a particular booster pack or tournament pack, he or she must call a judge. The final decision to replace or allow the atypical product is at the discretion of the Head Judge and the Tournament Organizer.
(My emphasis)
We don't need to precisely enumerate all of the variations on “very low-frequency things that might happen in a booster”. If it happens, the HJ and TO can apply their discretion, taking into the account of the degree of abnormality (an uncommon replacing a common being at the low end, and an entire pack of mythics being at the high end), the type of tournament, and in general what would be best for the specific situation.