1938-PDS and Type 1 1939-PDS dates came with the "Reverse of 1938 steps" These type of steps are wavy or ill-defined. Later in 1939, the US Mint made inprovements to the steps by making them more straighter. Those steps are referred to as the "Reverse of 1940" steps. As you can see in the picture provided, there must be full separation of the steps 4 and 5 under the 3rd pillar for the "Reverse of 1938 steps". The 4th and 5th step treads must run completely, all the way across from one side to the other without any bridging or melding between the two steps. Step one just beneath pillar 1 to the left of the Monticello is rarely ever visible. The overall look of the "Reverse of 1938" steps must meet the definition of those steps in character. And most, if not all of those coins, especially those that have been certified FS, do not meet this full definition of the "Reverse of 1938" steps, mainly due to the missing segment under the 3rd pillar. With 20+ years in collecting this series, a 1938-S in high grade with all 5 steps intact, is one of the most difficult dates to locate. From the picture provided, the separation under the 3rd pillar is there. IMO, this example grades MS66 with 5 complete steps.
Years back, in the 1970's, a group of Jefferson nickel (JN) collectors founded the FSNC (Full Step Nickel Club), they believed it was necessary to develope a method for counting the steps on the Monticello building. Reason being, there were several dates that were extremely rare or next to impossible to locate with 5 complete steps or with the full definition of steps. The 1938-S is one of them. Examples with 4.50 or 4.75 steps showing in the first 5 steps were considered to have full steps as long as there was a good quarter section or 2 of the 6th step visible, usually under the 1st and 4th pillars. In all my 20 years with this series, I have been able to locate only 3 examples of this date. I have never tried selling one until now. So if you were at a loss of words as to why I have such a steep price listed for this nickel, well.....now you know.
The 1939-PDS Type 1 JN with the "Reverse of 1938" steps faired worst with locating examples that showed the full definition of 5 complete steps. The 1939-S is the easier of the 3, followed by the 1939-P Type 1 and than the impossible 1939-D Type 1. If you happen to have a few years into this series and have a copy of the Analyst by Bern Nagengast, you will have a clearer understanding about those dates within this series.