Check your memory Thad, on that coin they weren't, the pencil eraser removed them if you'll recall (and can see in that image, above the date).
On copper yes, just about everything wrecks copperincluding Tarn-x and EZ-est, silver and gold are much more forgiving than copper.
I have removed "carbon" spots with an eraser. Never use pink rubber eraser though as most have abrasives in them, namely pumice. The white vinyl works fine though. If you use a draftsman's eraser shield and use a hole the size of the spot, you would have to know exactly where it was to find it. On a blast white coin, you can't, but on a toned coin it leaves a clean spot, more the reason for the eraser shield.
Copper coins and dip, specifically E-Z-Est (aka Jewel Luster), have NEVER been good for copper coins. Do a Silver Dollar.