A marathon runner came in today with a worn pair of GEL-Kayano 12 and a new pair of GEL-Kayano 14. Even though both shoes were sized the same length and width, they were entirely different shoes.
First, look at the outsole. The newer version is on the left and the older version is on the right. There is more soft EVA in the worn outsole on the right, which would cause the forefoot padding of the shoe to break down sooner.
If you have a history of ball of the foot pain (capsulitis, sesamoiditis, metatarsalgia), you will want your outsole EVA to be as firm as possible, so the left model would be better for you.
Next look at the upper. See how the older Asics on the left is wider in the toebox and in the heel opening or throatline? In this case, if you have a wider foot or a higher arch, the older version would be a better fit for you.
All in all, even though the name is the same, the versions are not. Bottom line – these differing versions are entirely different shoes. Although both are shallow in toebox depth, version 12 will work best if you have a wide, shallow foot whereas version 14 will work better if you have a narrow, shallow foot.
Beware of version upgrades and check them carefully. Even if you shoe salesman swears up and down there is no difference, don’t take their word for it, make sure with your own eyes and hands it is indeed the same shoe.