What makes a knife history correct. At one time all blade shapes have been used so how can anybody say it's pre 1880s or pre1750.
Are any of these designs pre 1840 design? How do you know?
So modern handles/grips not withstanding...,
You make an assertion that,
"At one time all blade shapes have been used"..., well then to your premise, how do
you know that?
How does anybody know?
As others have touched upon, they can only go by surviving examples and illustrations. Diderot's books are excellent sources for blade shapes, just as are recovered archaeologic examples.
Does that mean a blade shape that is undocumented for a specific era could NOT have been ? No of course not, but it's the duty of the historian to consider facts as information that is proven, not what could've been. It should also be noted that knowledge of one form of tech in one part of the world does not mean universal knowledge of that tech. In fact it's a quite curious phenomenon why folks widely separated yet having the same resources, don't develop identical material cultures....
You may also note that it may not be the silhouette of the blade that renders it "too modern" but the finishing touches and the steel that render it so. Reply #9 above pointed out a modern grind to the blade as a problem.
But beware of the mantra "You cannot prove it
wasn't there, so it must be OK". Because that's sophistry, and leads down a very nasty rabbit hole.
I'll give you a stock example of something that easily could've existed in the colonial world of the 18th century, but so far as we know, it didn't.
Stir Fry.
Chicken with brocolli
So in the British Colonies of the 18th century, they had carbon steel, and charcoal, and chicken, and broccoli and onions and rice and olive oil and salt, and pepper, and garlic, and even red pepper..., they even had contact with the Far East..., but, you never find any mention of stir frying food in a hammered, carbon steel wok (or any wok for that matter), and you don't find any colonial cooking books, or early American cooking books, with stir fry chicken and broccoli recipes. ALL of the necessary ingredients (OK so maybe not soy sauce) were in the colonies, and trade could've brought over the soy sauce, and sailors could've seen an Asian man or woman using a wok, and Asian men and women could travel, so the sailors wouldn't have needed to go all the way to China to see a wok used to make stir fry..., yet...., I think everybody would agree that a person at a historic site during a colonial history event, using a Wok to make stir fry chicken and broccoli,
while absolutely possible, would be incorrect to tell people it was an authentic colonial dish in the British Colonies.
And that's why we try to stick to what we can prove.......,
LD