On regular Cadillac, there are subtle differences from '59 to '60 (on like models).
Coach builder to coach builder the lower edge inward curve, wheel opening cutout, and latch changes. I do not know with certainty if there are additional changes from '59 to '60 as in regular cars but think not.
For years I had been told that '59/'60 professional car skirts are slightly longer than standard. Yet last summer with both '59 Series 60 Fleetwood and '60 MM skirts in my hand matched up, I can confirm otherwise. At least those two are the same length.