ebay is only one source for measuring the value of any coin...especially die varieties. With the sheer number of misattributed varieties that sell on
ebay regularly, much care must be taken to ensure you're getting accurate data. More than two thirds of the results would need to be thrown out because verification cannot be made with the images provided.
A few far better inclinations of value for die varieties would be to seek out the selling points of the authors of such material. I know of a half dozen immediately, but do not know the web addresses by heart. Searching the web would remedy this for you.
The values on coppercoins.com are not accurate primarily because the values of NORMAL coins in higher grades have gone up so much over time that keeping up with the premium plus grade value for die varieties is nearly impossible to do single-handedly, and certainly impossible to do for free. I gotta make money too.
I have been working on an algorithm that will recalculate the value of die varieties every time new price guide information is put into place for normal coins. It involves a premium curve and a multiplier for each individual variety - when the values of a normal coin for the issue are entered, the calculator takes off and supposes a value for a given die variety considering all the circumstances that caused its particular curve and multiplier are still in play. Those thing would have to be changed if the situation of the coin's rarity were to change.
While I can see the whole thing operate to some level of accuracy in my head that has never been put to keyboard or paper, I also know that my free time is very limited for taking on such tasks. I have a number of things I want to get done in this regard, and having a few typists would help a lot. If you are interested, send a personal email my way.
Eventually this information would be published in the form of a standalone guide to
Lincoln Cent die variety values, and it would also be included in my next book. Perhaps I can work out free copies to those who help in its production.