Yeppers , generally an error like that is spotted at the mint and destroyed.Hopefully someone better versed than i will chime in,from what i know though its pretty rare to find one.
Rarity depends on the denomination. I have at least 25 blank cent planchets, both copper and zinc. I also have a dime, quarter, and half blank planchet. I have not yet found a nickel or dollar blank, nor have I been able to find a silver blank.b They are fun to find.
The blank ones are actually pilot issues by the current government, sort of like the foreverstamp.....things get real bad you can barter in silver. (just kidding)