Notify Amazon if they sold the book to you that says 20 and only has 12 .
Be sure to count the stories and not just go by a list. Sloppy edit/proof may be the issue on the interior listing.
The Amazon ad can not claim MORE than was provided
from that site, the FTC gets real unhappy with them. (they can include un declared Bonus material)
Also note: US editions may be different than EU... (

copyright term variations. )