Now I see the point. Scar tissue can slow the digestion of insulin down. Due to the limited number of sites this can lead to absorption problems of the insulin itself.
So two conditions can develop with age: it can slow down digestion (spike comes later, less waiting time after the injection) and it can slow down the unfolding of the insulin action due to scar tissue (spike comes earlier, more waiting time needed). Well, hopefully they will neutralize themselves.