Early Parker pens had the unique patented "Lucky Curve" feed, which was an elongated conventional feed that curved back to touch the barrel wall.
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).
In mid 1934 Parker began marking most pens and pencils with a date code, both the barrel and the nibs were marked, but lacking a date code doesn't necessarily mean that the pen was made pre-1935, since many imprints have been worn off with use.
Hence a "47" marking on a 1930's pen indicate that the pen was produced in the fourth quarter of 1937, not 1947, which is a common misconception.
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.