Originally Posted by Caustic Man
The bolded statement is plainly untrue. These stylistic differences are precisely about the cut of the jacket and are major indeed. Just because both "fit" doesn't mean they are cut the same, as you go on to mention. I could go on ad-nauseum about the differences between the two eras but the simple question remains... "Would one look out of place wearing a suit from 1816 in 1916?" The answer to that is "Oh hell fucking yes"
. The OP's point, I think, is if you were to ask the same question about someone wearing a suit from 1916 in 2016 the answer would be "Yes, but less so"
. Could you get away with wearing a suit from 1916 today if you were to update the shirt and shoes alone? Yes, probably. The same cannot be said from the suit from 1816. This is 100% true and not up for debate from reasonable persons.
We are using "differences in cut" in two different ways. You are using it to mean "any visible differences in the outline and edges of the coat." That is the sense of "cut" which predominates when almost all tailored coats are lounge suits. Cut and silhouette are now commonly run together, because all lounges are cut in basically the same way. True, tailors have different systems of cutting lounges, but the same tailor is going to use the same cutting system to cut two lounge coats of different silhouette.
I am using "cut" in the sense in which it was used when body coats were live alternatives to the lounge. In that sense, it means "differences that require a different sort of cutting from the same tailor." You can alter a block pattern for a notch lapel to an M-notch without much problem. You can't alter a block pattern for a lounge coat to make it a swallowtail coat. You have to use a totally different approach to cutting the coat. In 1916, tailors and demanding patrons would not have considered the differences you mention to be differences in the cut of the coat. They would have thought them differences in what we now call silhouette, a useful term which wasn't widely available in 1916.
So I think you are running together cut and silhouette. You are right that men in 1916 wouldn't have worn a coat with a standard silhouette of 1816. But if you are also saying that they wouldn't have worn a suit with a standard cut from 1816, then--waist seams aside--the evidence is against you:
Apart from the waist seam, all you need to do here is lower the collar, turn over the top fronts to make lapels, swap the buttons, change the color, and voila:
And there were blue morning coats in 1916.