Not really a question of "WHICH" has or hasn't been "improved". The better question is how many times "HAVE THEY".
WHO originally constructed, then who made for a long time, and now who makes them; are all different answers.
One of the many reasons why lot variation is a very real thing, and why you should be mindful of it. Extruded powder has it's burning rate controlled by geometry and surface area. So if the production has shifted to a different set of equiptment, OR another supplier, it maybe slightly different than the last. Also with some of the extruded, many flavors WERE old surplus military powders. Whereas now they are newly(newer) manufactured.