I've had the very rare missing piece before, but have never received a piece that (according to the parts list) isn't even in the set! Bag 2 in the new Space Shuttle
Missing Piece Guarantee | BRICKNOWLOGY - Build Your Mind
Missing pieces on every order officially guaranteed by LEGO : r/lego
Amazon.com: Brick Loot Barber Barbershop Building Brick Set. 196 Pieces 100% Compatible, fits Lego and Other Major Brick Brands : Toys & Games
Bricks & Pieces - Customer Service - LEGO.com US
Star Wars Missing LEGO Pieces – PCX Promise Customer Experience – Jason Hewlett