Cartridge makers don't use exactly the same powders that you buy over the counter as a reloader. They do a lot more blending with each lot of commercial powder to get the burn they want. With reloading powders, they have to maintain consistency with previous batches at all costs. Promo loads will just about always contain the fastest powder possible for the load. The reason is that you use less of the faster powder than of a slower powder to obtain the same speed.
Less powder makes the shell cheaper.
Whether or not the fast powder gives the optimum pattern in that particular promo load combination is less a consideration to the manufacturers than the price. Promo loads do vary in quality quite a bit. It certainly makes sense to use them in your case. If only Remington Gun Club ammo is available at a good price in your area, then by all means use it for 16 yards. Just to a little patterning with your chokes to get the pattern you want.