cooking up a small theory that has been on the ingredients phase for a while anyway. some lines support it and then one line directly contradicts it but also its a little suspicious of a line anyway. 7.5 spoilers and theorizing below the line
I think Calyx was aware of the reflections before Halmarut told him and I also don't think shes the first ascian/ancient he had interactions with. He is a little too suspicious with how much knowledge he has, id say its close enough to rival an unsundered level of knowledge on souls/reflections. My personal semi baked theory is he either made contact with unsundered Azem to some degree or whatever memories they left embedded in the key/Ethos and were taught directly by them for a time.
I've been rolling around the idea the Azem found an apprentice pre-sundering anyway to serve as an actual threat level antagonist for the next arc and i feel like calyx is slowly sliding into this role. Halmaruts response to Y'shtola when asked if she was the one who taught calyx just feels... off? Halmarut's just like yeah sure it was me.
Shale also posits that Calyx knows how to make the key work but the magic itself is temperamental and not prone to listening even if done correctly. Not sure why sundered Halmarut would know how to use the key nor does she make any indication that she does. The last cutscene also confirms Calyx has his own agenda- and the data terminal in sol.9 goes out of its way to attach him to the concept of memories once again. There are also a lot of shots that seem to parallel him to the WoL/Azem in the last cutscene as well for... some reason.
Some select screenshots below
stormborns
janainaart
yousharknotpass
germansingergirl
pixelskylines
