Ron Guth: Among the fifteen varieties known of the 1820 Large Cents, three are Overdates. All three come from different dies. Newcomb 1 is known as the Large Overdate (referring to the size of the date); Newcomb 2 and 3 are Small Date Overdates. PCGS recongizes any of these three varieties as overdates.
Of all the 1820 Major Variaties, the Small Date is the least common, followed by the 1820/19 Overdate. The most common Major Variety, by far, is the Large Date.