How do you know the missing piece in the rim isn't a die defect? Why does a rim nick give the appearance of extra metal on the rim?
Because the hit displaced the metal, same as a dent in a car fender would, for example. I agree with everyone here so far- this particular coin appears to have a rim hit, not a cud.
I'm curious- does this coin have a mintmark? (Just a random question- it has nothing to do with the rim bump or anything else.)
It's an O mint mark. Do you know how much a CUD barber dime is worth? I have another coin that I'm pretty sure is a genuine CUD.
I posted 3 pictures of Barber Dimes that are part of my collection that I believe are CUDS. I'm positive at least 2 are CUDS. Not so sure about the one with the Reverse CUD. Please take a look. https://www.cointalk.com/threads/3-possible-cud-barber-dimes.319099/