(for pure speculation and reflection)
Well, I'd say "All that *is* rare," but anyway, your idea is one I think is worth considering. And Stein has something about cog being a Turkic god name, too.
Dear D. Many thanks, also for the English correction. “All people are nice. All is well.”
When I searched the OTDO (http://otdo.aa.tufs.ac.jp) I didn't find dkon-cog or dkon-chog one single time. I did find dkon-mchog (34 times) and dkon-mcog (6 times). What do you say to that?D
I am afraid in that case, I will have to discard my random thought. :-(
Dear D, A random thought is a terrible thing to waste. Especially since HH the Dalai Lama V rather consistently spells Rin chen as Rin cen, and Dkon mchog as Dkon cog, in His Record of Teachings Received. Still, for some reason I was of the persuasion you were thinking of a certain commentary called the དཀོན་ཅོག་འགྲེལ་, weren't you? -D
I think konchok is simply "rarity".
Yes, I think everybody, including myself, would think that dkon mchog means “the best among the rarities.”