Ron Guth: All of the 1873 Proof Nickels are of the "Closed 3" variety, meaning that the loops of the 3 were so close to each other that some observers thought the 3 looked like an 8. This same defect appeared on all of the earliest Proof coins of all denominations in 1873. Later in the year, corrected versions of many of the coins appeared, this time with a 3 that looked like a 3. However, none of the 1873 Proof Shield Nickels were struck with an Open 3; at least, none have been discovered so far.
As of December 2011, PCGS has certified over 400 Proof 1873 Nickels, mostly in PR-64. Cameos make up just over 15% of the population, but this may increase in the future because PCGS has not always recognized cameos. To date, no Deep Cameo Proof 1873 Nickels have appeared on the market. The finest 1873 Nickels certified by PCGS include 2 non-Cameo PR-67s and 15 PR-66CAMs.