I recently bought a seldom-used Aero (#1983) with a 7 rig. I began to notice that the upper portion of the sail was unusually curved compared with others, even while sitting next to them on the beach waiting to launch. No amount of adjustment of the sail controls or the batten screws would make it look anything like the others. Also, compared with other 7 rigs I had sailed, it was far more difficult to pop the battens after a tack or gybe, regardless of the adjustment of the set screws at the ends of the two top battens.
I then compared the top battens to those of a new sail, and found that they were substantially thinner, 3mm vs 4mm. That is a 33% increase, which gave them substantially increased stiffness. When I switched out the thin ones for thick ones, lo and behold the curvature decreased, and the sail popped across much more easily.
The Aero has had a number of tweaks to its design since it was first launched. All were publicly known, and none (in my opinion) had a big effect on performance. While the batten change is a positive one, it's hard to make the argument that it's not affecting the performance of older vs newer sails (independent of wear and tear issues). Maybe I've missed it (certainly possible), but I don't recall any publicity on this switch, nor do I know when it occurred. Another owner's older sail also has the thinner top battens, so my case is not a fluke.
Can anyone enlighten me on the history of this change?