Key Dates, Semi-Keys, Etc...

Most times it is just the lowest mintage for a series.

You also have to factor in availability, grade and other factors.

For example, In Lincoln cents the 1909 S vdb is considered the key.
But, IMO, a 1922 No D or 1955 double die would be harder to find and may cost
more in the higher grades.

Another example is Washington quarters, the 1932 D is considered the key.
The 1932 S has lower mintage, but being a S mint more seem to be have saved
by collectors back when they were first made. So depending on the grade
one can be higher then the other.

Best thing to do is look at a Red Book, it will show the mintage and prices.
By seeing which has the most value you can tell the keys for that series

Can't go solely on mintage. Seated dimes have many low mintage dates that are not considered keys, because there is not enough collector interest. So no buying pressure.

I think you take a series and look at a combination of mintage and availability along with collector interest and these all are important factors. There are also conditional rarities- common in low grades, but key or semi-key in higher grades- many Buffalo nickels fit this, some Morgan dollars also fit this.

I think in some cases, key dates are overpriced due to apparent scarcity that really doesn't exist, but the seller just doesn't want to sell it below a certain price. So many ebay auctions on keys/semi-keys anymore are buy-it-nows for inflated prices.


Here are some that I would consider key dates (not all-inclusive):

Cent: 77 Indian, 09S Indian, 09S VDB, 14D, 31S
Nickels: 13S Type 2 Buff, 21S, 50D Jeff (thought mintage is not super scarce- this may be an example of an over-hyped key)
Dimes: 16D Mercury
Quarters: 16 standing liberty; 32 D, 32S Washington
Halves: 21P 21D Walking Liberty halves
Dollars: 89CC Morgan, 93S Morgan, 94P Morgan, 28 Peace

Here are some that I would consider semi-key dates (not all-inclusive):

Cents: 08S Indian, 09S Lincoln (might be considered a key), 24D
Nickel: 26S Buff (lowest mintage, but apparently saved enough), 31S Buff (2nd lowest mintage, also saved)
Dime: 21P & 21D Mercury, 96-W Roosevelt
Quarter: 27-D and 27-S Standing Liberty
Half: 38-D Walker; 70D JFK
Dollar: Most of the CC Morgans, 21 Peace (could be considered key by many)

I think there was a thread like this before listing out all the semi-keys. There's tons, especially in virtually all of the 19th century series'.

! Dave, does that mean somebody might be making one?

It wouldn't take that long to run through a Red Book and pick them out. If you need help with the list, let me know and I'll do some! =)

As to a list of what is a key and what is a semi key coin, no such thing exists at all. You have to remember that such terms are what dealers usually use to justify their prices on coins. The quantity minted, grade, availability all mean nothing really. Mostly it's all popularity.
Examples are such coins as the 1931D Mercury dime with the 4th lowest quantity in the series minted. Yet no big value as with the 21 or 21D. Popularity.
The 1931S Lincoln Cent is another example of no popularity interest so although very low mintage, no big thing in values.
Then look at the 1955 Lincoln Cent Double Die. There are Double Dies in almost every year of the Lincoln Cent yet except for the 72 and the 83 reverse, not much is said about any of them. Popularity.
There are many coins like that where popularity makes them what they are and there is no list except in the minds of dealers.
Such things are true of many items all over the world I suppose.
With cars everyone wants a 1957 Chevy Convertible and it sells for a fortune. Yet many other cars have much lower quantities made and no interest compared to the Chevy. Example is a 1962 Chrysler 300 Convertible with only 123 made. So what, no one wants those. No popularity. I've got a car that only about 477 were made and probably couldn't sell it for the price of new tires. No popularity. Looks like this: