I've run into a few cases of insufficient canon information or inconsistencies in canon in regards to animal features, mostly on touhou characters.
There are multiple characters, who may or may not have animal features in canon. It is easy to spot if a character has animal ears, but a tail could be hidden under the character's skirt, so you can never tell if it exists or not.
For example, Inubashiri Momiji never has a visible tail. In print works, 2 out 3 times, she clearly doesn't have animal_ears either.
So if I see an image of her tagged with no_tail, I generally remove it. It makes me wonder if we shouldn't instead use kemonomimi_mode for when she does have those features.
On the other hand, Kaenbyou Rin was never depicted with tails and I removed the no_tail tag from her before a few times. Now, in the latest fighting game, she appears as a cameo background character with visible tails. I cannot tell how much freedom the artist had there (compare to the Momiji animal ears example above), but since this is the only kind of evidence for or against the existence of tails on her, (and since I cannot proof the non-existance of tails under her dress), I guess I need to go back to find the images from which I've removed the no_tail tag before and add them again.
A similar case for wings, but for wings. Shameimaru Aya is never depicted with wings in any of the games (i.e. they clearly do not exist). Wings on her have only been mentioned in text form once, and http://en.touhouwiki.net/images/2/2c/084.jpg shows other tengu with visible wings. That said, I do sometimes see that someone tagged her with no_wings, but since they seem to not exist at all in canon, or are at best modular, I removed that tag as well.
