And why twelve fundamentals of physics (if that is the correct classification), but not a numbered list of anything else?
See, that's the issue. We have no way of knowing if it was a list of 12 physics propositions or 12 ways of sensing things or 12 basic particles or 12 fill in the blank. All the text does is quote 1 to 3 sentences (the text is unclear) that were somewhere "in the 12 basics". Whether that or those were actually "in that list" or whether they were contained in an explanation of the 12 or in the introduction to the list, we have *no way* of knowing.
PS
Quote from Cassiusnot a numbered list of anything else?
We have no way of knowing how many lists, summaries, etc that Epicurus wrote and shared. We've lost too much.