No rain. Thanks for the link. The initial article I read was in the New York Times, which usually is reliable. It links, in turn, to the article in the J Anat, which is highly respected, peer reviewed. Said article noted right away that the structure in question was first described by a French surgeon in the 18th century. And concludes:
"By providing a detailed anatomical characterization of the ALL, this study clarifies the long-standing enigma surrounding the existence of a ligamentous structure connecting the femur with the anterolateral tibia. Given its structure and anatomic location, the ALL is hypothesized to control internal tibial rotation and thus to affect the pivot shift phenomenon, although further studies are needed to investigate its biomechanical function."
In other words, the NYT and I were using "discover" in a casual way. In reality, things are seldom literally discovered in science, but on the other hand, a description that differentiates a new entity that was formerly lumped with others, or misunderstood, along with a new functional explanation that's testable, is pretty close. That's more than a re-description.
Modern physics, paleontology, biology, and astronomy provide plenty of obvious examples. Plenty of fossil species have been discovered in material collected years ago, measured, catalogued, and left to collect (more) dust in a museum drawer. A fresh pair of eyes, a more careful set of measurements, a more relevant theory, and whoaah! a new ancestor. Same happens in zoology all the time when one species of say fish is observed carefully, perhaps some DNA is sampled, and discovered to be two species. Einstein didn't deal with much that hadn't been first described in the 19th century. But he provided a set of explanations and testable predictions that reshaped how we interpreted the old data. He was the discoverer of relativity. Watson and Crick weren't the first to describe DNA. By far. But they were the first to look at the descriptions and realize what they were looking at, what the implications were. So the Nobel committee considered them the co-discoverers.
When I taught anatomy, the ALL, if and when we found something that must have been it, was considered to be a normal variant/accessory of the FCL. That is, we didn't see it as having its own function and own evolutionary backstory. We literally didn't see it. The ALL is not indicated in any anatomy text or atlas I own, or am familiar with. So to argue it's actually a new ligament with its own biomechanics is pretty close to a discovery, actually, whatever your link says.