I'm not sure this is a "bare passive" like the beginning of "The day's work [being] done, they made their way back to the farmhouse," one of the bare-passive examples at your link. An analogous construction would be, "The points already [being] made, I ceased harassing the ignorant". But in "In addition to the points already made" this case "the point already made" is not a clause; it's a noun phrase, the object of the preposition "to". Its head is "points", and I believe that "made" is modifying that head.

Can you insert an elided copula into it without changing the meaning and grammatical structure? I'm not sure. I don't think so. I think "In addition to the points already being made" means something different: the object of the preposition "to" is now "being", and we are going to discuss things in addition to that state of affairs, perhaps other things that have happened to the points (being sharpened, perhaps, or being discarded), not things in addition to the points.