Well actually there is a bit more to it. The mash bill is EXACTLY the same. The Van Winkles have first choice of the barrels they want and they also determine where in the rack house the barrel is stored. They always age in the very lowest levels of the rack house. So it really gets down to cherry picking the best barrels to begin with, aging in the right place and then choosing which of those they want to put their label on. Keep in mind that there are only 3 Pappys....15, 20, and 23 year old. The rest are labeled Old RIP Van Winkle or Van Winkle Family Reserve (includes 12 year Lot B and the Rye). People tend to call anything with the Van Winkle label on it a Pappy. On one of the bourbon forums I am on there is a recipe for combining 1 bottle of OWA and 1 bottle of Weller 12 to make your own Pappy 15 taste like. It's pretty good actually but too much of a hassle as each component part is pretty darn good by itself. If you just have to have a decent wheater and can't find Weller's or Van Winkle then try Larceny or go to Kentucky and buy some Old Fitzgerald Bottled-in-Bond.