Disclaimer: This is just a guide to give you an idea of what your coin might grade. Often coins will grade higher on one side vs. the other. In example, it's possible for a coin to grade G4 on its obverse, but grade VG8 on its reverse. Also, this guide is not a claim that one's coin will obtain any grade listed if submitted to a third party grading service.
Since most of us will never own a 1792 Half Disme, and that fact that only an estimated 400 examples have survived, then why have a grading page for them? I can give two of many reasons for this and one is that not too long ago a person found one in Philadelphia while metal detecting, so you just don't know who will find or end up with a raw example.
Anywhere from 1,500-2,000 were minted, so there's possible a few more to be discovered. Also, who wouldn't be interested on the grades and images of the first U.S. coin minted? I know I do and there's historical mystique surrounding the minting and purpose of the Half Disme. If you're interested read this 1792 Half Disme History, Facts & Mystery