Just in general observations, the older balls used harder coverstocks. Case in point, my old Zones which I still love. Red Alert, Danger, Demolition and Shock. These balls still operate fairly close to the levels of the times that I first bought them. Having said this, it is also quite a chore to alter their surfaces to the levels that are needed on today's lane oils. It can be done, it is just more difficult to do.
Today's HP balls are much more sensitive; much tackier; much easier to alter, and as such much easier to lose performance strength more quickly. To me this is a sure sign of softer and more elastic polymers, and greater and more severe surface topography with these newer pieces. It is a curse and a blessing rolled into one!
It's kind of like driving a BMW or Mercedes. You love the looks you get when you drive it. You love the performance when you drive it hard.......but you hate the bill when you have to maintain it!