IHC Experts- DD or Strike Doubling?

I have 2 IHC that have DD or SD on the 'OF' in US of A.
1 is a 1872, the other 1864.
Is there reports of DD in those years?
1864

1873
1 is a 1872, the other 1864.
Is there reports of DD in those years?
1864
1873

0
Comments
"During this time period, some outline images can be seen on the letters of the legend for many of the 59-86t1 dies, These images, occasionally mistaken for double dies, are believed to have been caused by extra metal being left at the base of the letters of the ring punch, or that the legend was simply impressed to deeply into the die,...... " L. Steve & K. Flynn