The NGC Universal ID is a four digit alphanumeric that groups coins based on a unique combination of date, mintmark, denomination and striking process (MS, PF, or SP). These IDs are a simple organization of all coins prior to variety attribution and grading.
Q. David Bowers' useful Guide Book of Double Eagle Gold Coins neatly divides the 1850-1933 double eagle series into six major types, three each in the Liberty Head and Saint-Gaudens series. The Liberty Head Type One pieces, running from 1850 to 1866, are the No Motto coins with the denomination abbreviated TWENTY D. The Type Two coins, from 1866-1876, are With Motto, and the denomination as previous. The Type Three coins, the largest and most plentiful group running from 1876 through 1907, are With Motto, and the denomination spelled out in full as TWENTY DOLLARS.
Numerous shipwreck hoards--the S.S. Central America, the Brother Jonathan, the S.S. Republic--are responsible for several recoveries of Type One double eagles that are, in many cases, in pristine Uncirculated condition. Notable is the fabulous recovery of thousands of 1857-S double eagles (along with various other dates), including many Gem specimens, from the ocean depths. Those coins were aboard the S.S. Central America when the ship foundered in a hurricane off the coast of Charleston, South Carolina. Today specimens of several Type One issues are widely available up to Gem Mint State, albeit for a price.
Gold, silver, and paper money circulated in the United States at par with each other beginning in December 1878, after the economic imbalances created first by the Gold Rush and then the Civil War. Double eagles circulated freely, although more so in the West, since paper money was favored back East. At about the same time that the Bland-Allison Act of 1878 encouraged more domestic use of silver, other nations were abandoning the silver standard in favor of a gold one. International bankers feared the United States might settle overseas debts in silver, and accordingly a vast outflow began of newly minted double eagles, along with older circulated pieces, usually shipped in cloth bags. Many hundreds of thousands of Type Two and Type Three Liberty Head (and Saint-Gaudens) double eagles were exported overseas, to be repatriated later. Such pieces were usually handled with little care and were subject to extensive bagmarks, even when technically Uncirculated.
While Type Three double eagles can occasionally be found in pristine Mint State, most examples are rare above MS62. Type Two double eagles in Mint State, however, are far rarer. Bowers says of the Type Twos:
'Mint State examples can be acquired of most issues, but nearly all are in lower grade ranges such as MS-60 to MS-62. Some of these are from foreign hoards, such as 1867 and issues from 1873 onward, and most are extensively bagmarked. ? Nearly all Mint State coins are heavily bagmarked, but several issues are often seen MS-63 or finer, these including the 1873 Open 3, 875, 1876, and 1876-S.
'Quality can vary considerably, including among certified coins, and close inspection is advised when purchasing. Gem Mint State coins with good aesthetic appeal are exceedingly rare, far and away the rare of the six major double eagle design types.'
It is interesting to note that Bowers does not even mention MS65 Type Twos, and double eagle aficionados will attest that the difference in aesthetic quality from MS62 or MS63 is (or at least should be) a long one indeed.