I'd argue that the quill pen was a special case. As you point out, it was an intentional anachronism to communicate a certain point. This was not the case with, e.g., the floppy disk, the notepad, the contacts book, etc. Everyone knew what the quill pen was because it was still frequently seen in portrayals of the olden days when it was used; even today, portrayals of Victorian England in Doctor Who or Revolutionary America in Hamilton inevitably show a few quill pens in use. But the reason people recognized floppy disks, contact books, and notepads was because they were still in active use at the time.
You point out that while the quill pen was long outdated when it was first used, "everyone still recognized the contents of that icon", but that's exactly the problem that the GP and GGP are pointing out: more and more of the old skeuomorphic icons reference real world icons that younger users (and indeed some older users) actually don't recognize. Notepads, sure, we've still got those; contact books, eh, you'll see them once in a while, but tbh when I see a bare "contact book" icon without a label it occasionally takes me a second to figure out what I'm looking at; floppy disks, as has been argued to death, are entirely a thing of the past, with the exception of old systems and archives still in use in dusty university basements. Young users today essentially just know the image of a floppy disc as "the save button" without any skeuomorphic rationale backing it up.
The skeuomorphic link between computers and the physical objects we use is is constantly degrading, to the point that using skeuo icons can sometimes actually inhibit the user experience and slow the user down while they try to figure out what they're looking at. We have common patterns emerging with no or very little connection to the real world; a great example would the "hamburger" menu button. If there's any metaphor there in the user's mind, it's to the row items that will appear when you click on it, not to anything physical, yet it's perfectly comprehensible to anyone who's been using digital devices for any length of time.