Missing Lego instructions? You can download them online for free
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
Bricks & Pieces – AG LEGO® Certified Stores
LEGO Bricks (You Choose) Small Detailed "Missing Any Little Pieces?" | eBay
Missing Lego instructions? You can download them online for free
LEGO pieces missing or broken? What to do?
Missing pieces on every order officially guaranteed by LEGO : r/lego
Can You Order Missing LEGO Pieces? If So, How? - VerbNow
Where to buy individual LEGO bricks – Blocks – the monthly LEGO magazine for fans
LEGO Brick 1 x 4 x 3 with Head, Cat, 'MISSING' Sticker (49311) | Brick Owl - LEGO Marketplace