I.W. Harper 15 Year Straight Bourbon

IW Harper 15yr was export/available in Japan only until 2015.  Distilled at the New Bernheim Distillery, aged in Stitzel-Weller Distillery warehouses, and bottled at Diageo’s Tullahoma, Tennessee facility.  Mashbill of 86% Corn, 6% Rye, 8% Malted Barley.  Yet, the mashbill for the 'original'/NAS IW Harper is different.  Hmm.  Are there different mashbills for each marque, or is the source for the 15yr running dry and to be someday replaced by the 'original' mashbill?