Key Date

So as a new person I'd just like to say Welcome one more time.
As to your question. It's a really tuff one in a way. What some think of as rare or key coins are the ones with low mintages. Some just think of a key coin as one they just can't find. Regardless the thing you should do is to find a copy of the Red Book on coins by Whitman Publishing. In there on any series you could see what are considered the key dates by the prices or quantity minted.
If you do not want to spend money on that book, just go to the many web sites where they list coin prices such as the PCGS web site or Coin World web site. Then by the prices you could see which ones are the keys.

I'm kind of with what justcarl was talking about. Key dates can actually be relative from series to series.

There are those famous key dates that are very well known, like the 1909 S-VDB Wheat cent or the 1916d Mercury dime. But you can also define 'a' key date as just being a coin which is key to that specific series. Such as the 1970-D Kennedy half. The 1970-D is not hard to find, very readily available in high grades, but has the lowest mintage of any other coin in the series* so its considered "key" to the series.

Low mintages usually determine whether the coin is a rare or key date, but there are many exceptions. Such as Three Cent Nickel pieces. Many Three Cent Nickel pieces have very low mintages, but the lack of popularity of the coin doesn't make the pieces rare or key at all. Popularity in the series can have a lot to do with the price. Another example, with the 1909-S-VDB Lincoln Cent and the 1928 Peace dollar. There was more than 100,000 more S-VDB's minted than the 1928 Peace dollars, but the S-VDB is worth like 700 dollars in G condition whereas the Peace dollar is worth $300 dollars in the same condition.

I'm not so sure I know what I'm talking about so maybe somebody else can give you some better advice.


*excluding the 2008 mintage numbers for the Kennedy halves.

It all depends on your budget and what level of preservation you want to go with. Lincoln cents are a great place to start with some challenging keys and semi-keys. When it comes to the keys (1909-S V.D.B., 1909-S, 1914-D, 1931-S) & the semi-keys (1911-S,1924-D to name a couple), these can get pricey especially in higher grades. Then there is the subject of authenticity. The 1909-S V.D.B. & 1914-D are counterfeited quite often so unless you are trained on spotting the diagnostics of the real deal, go certified. Good luck!