I just wanted to add something else to this...
While they are part of the Circle of Knowing, I don't think Y'shtola, Yda, Papalymo, or Thancred are ever mentioned with the title of Archon. The only two within the Circle of Knowing to hold the title of Archon are Loiusoix and Urianger. On many occasions do NPCs refer to Louisoix as Archon Louisoix, much like NPCs reffered to Ahldbhar as Archon Ahldbhar. Urianger gets the same treatment.
The other four in the Circle of Knowing may just be pupils of Louisoix, hence why they seem to know less than their leader and why Urianger and Louisoix seem to know quite a great deal as to the things happening in the realm - They have previous experience with it.
As for the matter of Ascians, grim reaper looking things, Paragons, and the NPCs we've encountered so far, I'm of two minds.
The first is that SE may have simply retconned the lore of the Ascians since 1.0. Remember that the 1.0 main story line was established when Tanaka was in charge. The fall of Dalamud and the release of Bahamut wasn't decided until Yoshida took the reigns. This wouldn't be the first time SE has retconned things into the lore. Due to the changes in the lore and the differences in direction, the grim reaper Ascians may have simply been updated into being the Ascians we see now in ARR. The Elezen who we encounter that we've been led to believe is an Ascian as well may have been retconned into being a hooded mage too. We don't know until we can get confirmation (if we ever do that is) on this bit of lore.
My second stance says there is a hierarchy of some sort in place. I believe Moose touched on this theory in another thread, but let me throw in my own thoughts into the mix.
What if...the grim reaper-like Ascian we see in the 1.0 main quest line is a much much older Ascian, or even more, one who did not complete their blood pact with the demon lords? Think Fal'cie and L'cie. In a similar manner where if a L'cie does not complete the focus granted to them by the Fal'cie, they become a C'ieth. Assuming Ascians are immortal sorcerers who made a pact with the demon lords of the seven hells, what if an Ascian who doesn't complete his blood pact turns into one of those things? That could mean that the supposed Ascian who steals the horn in 1.0 was a newly inducted Ascian and the two Ascians we see might be Ascians who've been around for awhile now. It's just a theory with no substantial evidence, but I thought I throw it out there in the case others could add on to it or dismiss it.