Challenger Shaker hood question

Ive seen a few Shaker hoods that have a center rib in front of the opening , this rib follows along toward the front and stops where it widens for a Pentastar to be mounted on it , Ive seen another ( in pictures ) that doesnt have this center rib and is flat with no Pentastar . Is this a model year change ? or possibly a stock flat hood that was made into a shaker .
Author: Hemi T/A