In addition, I have been able to inspect a demonstrator with the "1" imprint by the clutch ring and a rounded blindcap.In addition, in most, but not in all cases, the "first year" pens will have jewels made of aluminum.
It seems as it Parker ran out of cap jewels first, and continued production with whatever was available.
On some pens, Parker also appears to have used silver for the jewels, as one does find "first year" pens with jewels that have that unmistaken yellowish silver patina or heavy tarnish.
Most likely this was due to the pre-war constraints on strategic materials.
The Parker "51" commonly referred to as a "First Year" pen is really a pen from late 1940 through 1941.
They can be easily distinguished from later production by several unique characteristics.
All pens of this period are double jewels, meaning that they have a decorative "jewel" at the top of the cap and at the end of the barrel.
The imprint on the majority of these pens is at the end of the barrel, near the decorative "jewel", all in one line.
They may or may not have a "1" datecode after the imprint.
Some collectors speculate that the ones without a datecode are really pre-production models from 1940.
Another explanation may be that they were never dated or that the datecode wore off (on most instances the datecode is lightly imprinted to begin with).
It should be noted that some examples have been found with the imprint up by the clutch ring, with a datecode of "1".