In regard to the Breen, I would note that Star Trek Adventures: Klingon Core Rulebook says "They only
present themselves to non-Breen in full-body suits that hide
their identities, and their bodies disintegrate when they die
while wearing those suits. While this is an admirable trait – it
means Breen cannot be taken prisoner, an attitude in line
with the teachings of Kahless – it has made it impossible to
determine the true face of the Breen." This is a pretty cool explanation for how Worf could be right even after Kira and Dukat stole their suits.
I know STA isn't canon but I still like this reasoning.