The best way to tell is the rims near the edge of the coin.

Note the roundness at the edge of the coin. Those are formed by the collar and the die. It rounds over naturally because of these two. The line around the coin next to the rim is the edge of the die.
If you had a strong struck through they should still be strong on the coin when looking at both sides. Here is a struck through:

Bot how they are still strong in most areas despite the struck through? Small areas might be affected a little, But they are mostly there. That is what you look for on a mint error.

On this one the struck through cover the full obverse, but note the reverse. They are firm and completely there.

The affected area are weakened, but the reverse and the affected areas are fully rounded.
Edited by coop
02/12/2015 11:32 am