Question For Jefferson Nickel Expert

I am not an expert but I can answer your question.
In 1938 the steps were weak and wavy. Some of the 1939 Phila D and S had this type and also had the reworked reverse die used in 1940.
The 1940 steps are much sharper and straight across. There are 1939 proof nickels with both styles with what I think without looking makes the 1939 wavy steps proof easier to find.
There are some RARE 1940 proof nickles with the wavy steps too but they are RARE and expensive.
There are no 1940 circulation business strikes that I know of from 1940 with the wavy steps on the reverse.
I have the facts in my book on which 1939 issues are tougher to find but they can be fairly easy to find in both styles.

Check this page out and click on the easy to find coins listed such as 1939 Jefferson with the reverse of 1940. This will visually answer your question.
http://www.pcgs.com/setregistry/all....aspx?s=2415

The steps are not always worn away, quite often they were incomplete when they were minted. Full step 1938 nickels are elusive and so are the 1939. This is partly the reason for the reworked dies of 1940.
Actually, I think full step nickels from 1938 and 1939 with the steps of 1938 are undervalued.