Hi,
That's easy, don't put any back in circulation:-) They are all worth more than face to die variety collectors. A common
DDO half can be a $2.00 coin and a rare high grade, well struck, early die state one could be a multi-thousand dollar coin.
The values are always tough to assign unless something has a proven track record with regard to sales. Some coins like a 1969 S
Lincoln Cent Doubled Die Obverse for example has a fairly proven track record. High prices are achieved at auction. If , however, a bag of unsearched 1969 S cents turns up with 100 or more of these coins in it, the prices seen now will implode if all the coins came out at once.
With Kennedys and with Ikes, for example, I think we are just touching the surface as to what's out there.
I don't think we have a complete picture of the different die varieties that are in those two series of coins.
As more and more people start looking through halves and start finding more die varieties, things will begin to fill in some of the blanks, so to speak and we'll have a better idea on values.
Take the 1974 D
DDO Kennedy, a coin where more and more keep showing up, the prices have come down quite a bit over the past five years or so.
Anyway, keep whatever you find that is truly a die variety.
Also, don't neglect to look at the reverses of all halves that you search. What I key in on is clearly doubled star points and rays. Then I look for notches and splits on the lettering.
Have Fun,
Bill