Mark Ashurst-McGee asks about the uniformity of the Golden Plates in eyewitness accounts, even though they contain both Mormon’s abridgement and Nephi’s small plates, and this is in fact genuinely weird.
As I’ve mentioned, my mental models are based on medieval and early modern European books, where it becomes quite common to bind disparate printed books or manuscript quires into the same volume, but it’s only possible if the various parts are all roughly the same size. This becomes a lot more likely after 1400 not with print, but with the widespread use of paper, which was printed in standard-size sheets. The distribution of parchment manuscript sizes is pretty continuous, but paper manuscripts are strongly trimodal, generally corresponding to octavo, quarto, and folios. So if you take two quartos, chances are pretty good you can bind them together after trimming the margins, usually without losing much or any text. With parchment, though, there’s not any kind of standardization, so the parts often don’t fit as neatly.
So are golden plates more like paper produced by early industrial processes in Italian paper mills, or more like parchment produced by local craftworkers? I think we have to say parchment. In the two cases of plate production described in the Book of Mormon, Nephi and Mormon both state they’re creating plates for their own use, so we have to imagine this as individual and amateur production, which seems at first glance unlikely to result in a perfect fit.
Gardner takes the uniformity of the plates as described by nineteenth-century eyewitnesses as evidence of a standardized Nephite plate size. A conscious standardization seems unlikely to me, since we don’t find this with parchment manuscripts. And I don’t expect many sets of metallic plates were actually ever created in any case.
Did Mormon just get lucky? Maybe, but that seems like incredible luck. I don’t expect writers would leave wide margins on a surface as valuable and difficult to work in as a golden plate, and I don’t know if it would even be possible to trim a stack of golden plates to fit the dimensions of Mormon’s plates.
Mormon may not have needed quite as much luck as it seems at first, however. If you pick any book off your shelf, the ratio of height to width of one page is very likely to be somewhere around 1.4 to 1. (An 11×8.5” sheet of paper is just under 1.3, for example.) This ratio has been incredibly stable for a long time. In parchment manuscripts, it hovers right around 1.4 for over a thousand years, even without any conscious act of standardization. There are certainly exceptions, and as mentioned the widths and heights are all over the place, but the average ratio of height to width changes very little without anyone ever decreeing a standard.
So that means if something similar applies to Nephite plates, Mormon only had to get lucky in one dimension, not two. And if there can be an unconscious standard ratio, perhaps there was also an unconscious standard size, the sense that a normal writing surface should be, say, about as wide as you can extend your thumb and forefinger (which would fit eyewitness descriptions of a width of around 7 inches). A few basic standards, which doesn’t seem impossible based on what we see in medieval Europe, might get you close enough for careful trimming of the margins to take care of the rest—if that’s even possible, of course.
A thousand years is still a long time. In addition to the considerations already mentioned, we can’t verify that Mormon attached Nephi’s original small plates rather than a copy produced centuries later, still proclaiming that I, Nephi, made these plates. (That’s not at all unusual for the kinds of books I usually deal with.) I suspect it’s actually more likely that’s the case, so there would be much less separation between the small plates as an artifact and Mormon’s own time, which may also increase the likelihood of physical similarity.
Another possibility is that when Mormon says “I shall take these plates…and put them with the remainder of my record” (Words of Mormon 1:6), he’s describing an act of textual copying rather than physical combination. That strikes me as a real possibility as well.
 For more on this and the source of the first image, see Jonathan Green. “Reading in the Dark: Lost Books, Literacy, and Fifteenth-Century German Literature,” Seminar: A Journal of Germanic Studies 52.2 (2016): 134–54. https://doi.org/10.3138/seminar.52.2.3.
 Cf. Gardner, Labor Diligently, 138.