If I'm remembering correctly, in the guide to the dragon world it mentioned that RainWings used to have something along the lines of an assassin training program. Until one of the queens shut it down to try and get the RainWings to transition into a more peaceful lifestyle.
Something I'm considering for my book three rewrite is to include something like that. I'm not 100% certain if I will include it or not, but if I do, the idea I currently have is that some RainWing assassins were upset about the training program being shut down and decided to start their own training program in secret, or something along the lines of that.
Eventually, by the time of book 3, it's an open secret sort of thing. It'd be nearly impossible to find a RainWing who didn't know about its existence, but it'd be just as hard to find one who actually knows someone who's a part of it.
If anyone has any thoughts on this, feel free to let me know.