Let's set something straight about nib terminology. Some people refer to the hole at the end of the slit in a fountain pen nib as a "vent hole", but it doesn't "vent" anything. Most fountain pen nibs have them, but they would do just fine with a nib without a hole. Okay, some air goes in through the hole, but enough air also burps in through the slit, and gets in all around the nib and feed that it almost makes the hole superfluous. And an open nib in a penholder, or dip pen doesn't need any kind of "vent hole" at all, although most steel nibs still have an aperture at the end of the slit.
This is what the so-called "vent hole" really does. The aperture in most steel nibs serves the function of adding flexibility to the tynes of the nib, so they should more rightly be called "flex holes". This is also true for gold nibs, but in most gold nibs the aperture serves the extra function of stopping the slit in the nib from splitting further under the pressure of flexing, so they should more rightly be called "anti-split holes". Sometimes even an aperture won't stop a slit from cracking further. Drilling a hole at the end of a crack to stop it from spreading any further is an old machinist's trick. It is used by a lot of pen repairmen to repair cracked cap lips. They drill the hole, then fill the hole and crack with the repair material of their choice. There is a third function that the aperture serves, and that is the purpose of providing good looks. Fountain pens with nibs with apertures are a longstanding tradition, and some people think that they just look better this way, so they should more rightly be called, I don't know, "pretty holes"? ;~)
As for the 1917 catalogue listing of the nibs without apertures, this is to be expected. A product will always continue to be produced as long as some old fuddy duddy keeps asking for it. Eyedropper pens were produced by Waterman well into the 1940s. When I said that it was a "good guess that it predates about 1890", I wasn't just referring to the nib. I was also taking into consideration the style of the pen case in the original posts.
Please notice that I didn't use the term "vent hole" even once in this post. I merely mentioned it. ;~)
George Kovalenko.