1873 Two Cent pieces come in two formats: Open 3 and Close 3. The Close 3 variety (sometimes called Closed 3) was the earlier version of the two and was replaced when complaints came in to the Mint that the 3 looked too much like an 8. The Open 3 variety solved the problem. For the Proof version, the Open 3 is considered a Restrike.
The mintage of the Proof 1873 Two Cent piece with the Close 3 is only 600 pieces. Because this is a Proof-only date, demand is very high. Numerous high-quality examples exist, but Gems in full Red color are the most highly prized. As an illustration of this point, a PCGS PR67Red example sold for $52,900 in 2010.