There are only 3 die pairs for 1877
IHC proofs. All have the bold N reverse. I believe that this is die pair #3. Pieces struck from this die pair were only struck once and have thin denticles especially on the right side of the obverse. The weak strike make it very difficult to identity coins from this die pair as proofs except for certain markers for the die pair, such as the date position and very small die lumps on the neck. Could possibly be a die crack on the reverse but Snow makes no mention of it.