Alex, your pen looks like it's in fantastic condition. Congratulations!
It's hard to date these pens specifically because they were made for a number of years. We don't really have any concrete information on when certain nibs styles and imprints were made either, just general evidence of eras. As I recall, the 42-1/2 came with a Lucky Curve 4 nib, so I believe your pen to have a replacement nib, keeping us from using that to date the pen. The 42-1/2 was introduced in the early teens, making it harder to use the barrel imprint to try to date the pen through the inclusion or exclusion of patent dates in the imprint.
Can you tell us what the barrel imprint says, especially the patent dates noted?