Frequency of error (IMO) is the most likely factor that determines which errors are valuable and which one's aren't. For example, the average run of the mill greasers are frequent so aren't worth that much. On the other hand, if greasers only happened on only one coin maybe once every 10 years, they'd probably be more valuable when found.
Frequency of the error is the “supply” part, don’t forget the “demand” side...ultimately, if no one wants the error then there is no demand = no premium...imo...Spark
@Don northrup ...Welcome to Coin Talk. As a new member, you should learn to check the age of the post first. But, don’t feel like the Lone Ranger, all of us have made this mistake. You responded to a guy last seen here in 2013, who was 65 yo then, he would be 73 now, if still alive. Here is a website that will be useful to you: Wexler... doubleddie.com. Many articles there to help you, if you didn’t already know...imo...Spark