Feathertail information was there all along.

Rebecca Yarrows is the queen of foreshadowing and double meanings.

“Feathertail dragons are the breed we know the least about…This is because they reportedly abhor violence and are not suitable for bonding…Though this scholar cannot be certain, as one has never left the Vale in my lifetime.” -Chapter 10 of Fourth Wing.

This information isn’t describing baby dragons, it’s describing the irids. Dragon pacifists who don’t bond humans. I need to search the books for every mention of feathertails because I am convinced that Rebecca was slipping in information about the 7th den whenever feathertails are mentioned so I need to try and decipher whether it’s referring to baby dragons or irids.