Is this date anomoly called a 'slider', as in the planchet slid a little during the striking process? Tommy, if you shoot your picts with non-direct sunlight or with a not very bright 40 watt light bulb then the light and darks of the shiny coin picts will be way less harsh, which will show the details much more clearly. I've adjusted your pict and even now it's tough to see any doubling.
I have never heard that term before. The correct terminology is Strike Doubling.. Not a true Doubled Die Strike
We see these 1969 S threads like 2 or 3 times a week. Everyone thinking they have the "Big One".. but no This is it -
Tommy, when you see the S is also doubled, that's a clear sign it's strike doubling, because the S was added to the die after the die was made. That's pretty prominent strike doubling, though, on the date and S.
