So some legendaries are locked behind complete rng, 3rd upper reaches before 2nd Skoldus hall in Torghast
I was looking forward to finally being able to pvp on my lock alt properly but apparently that's not to be as Skoldus is still not available. Instead we got the upper reaches for the 3rd time with only 1 week in between the last time.
So yeah seems there is no real system to and it's just a 1 in 3 chance that the wing you need shows up.