HITEN C UDESHI

Hi,
While I was going through your website for valuations of Gold Coins of USD 20 for a few years like 1869, 1870 etc it had 2-3 different values
eg : year 1869 : 175 130; $ 1950 and same year
proof $ 2,10,000

Year 1870 : 155,150 ; $ 2000 same year
CC, 3789 : $ 275000
Proof,35: $ 215000
So what are these different values and how can I know the value of the coin I pocess.
Thanks,
Hiten