There are many such things which we do not about silver coins. Do you know that:
Privately minted silver coins are commonly called "silver rounds" or "generic silver rounds". They are called "rounds" instead of "coins" because the US Mint reserves the use of the word "coin" for Government Issued circulating currency, such as all common coins and the American Silver and Gold Eagles. The privately minted "rounds" usually have a set weight of 1 troy ounce of silver (31.103 grams of 99.9% silver), with the dimensions of 1/10 inch thick and 39 mm across. These carry all sorts of designs, from assayer/mine backed bullion to engravable gifts, automobiles, firearms, armed forces commemorative, holidays, etc.
Many factors determine the value of a silver coin, such as its rarity, demand, condition and the number originally minted. Silver coins coveted by collectors include the Denarius and Miliarense.