Isyth

the oldest dragons in my clan that are also the oldest feeling are Aoki, my three clan leaders, and two mated pairs of Imperials... one of the Imperials is Arcane so she might join Aoki in the "actually knows very powerful magic and isn't telling you" club. she knows much more than she's letting on anyway. Isyth on the other hand came to Shadow because it's relatively peaceful in comparison to the mad science (magical) flight of whatever the Arcanist is doing. her mate and the other old old pair of Imperials probably know but she's not telling anyone else. including Aoki. they just have a silent "you too huh" knowing stare relationship with each other instead.

StrawberryAlex: It'd also make sense for Arcane to know these things if you're following my sort of lore! In my lore, Arcane and Light both have heavy documentation on old powerful magics, but Arcane still regularly attempts to study/use them for study. At least when it comes to magic tied to their element. Following my lore layout, your Arcane Imp may have been a well respected older Imperial that had access to such material and was allowed to leave the territory knowing such information due to built up trust with those around her.

StrawberryAlex: There's actually an entire chain of islands that are quarantined off from non-Arcane dragons solely because that's where they test such magics out