Easy to tell if ring has slipped on hub:

Early dampers had O degree mark that is 2 degrees off from the centerline of the keyway.

69 and later dampers had the 0 degree mark located 10 degrees off of the centerline of the keyway.

You can eyeball the keyway to timing mark,on an 8 inch OD damper, one inch on the circumference equals 14.3 degrees (appx). Therefore, if the timing mark relative to the keyway centerline is off by an inch, something has slipped.

This test requires no Snap On tools but I bet they make one for it.