Fritz Kreisler was an Austrian born American composer and violinist. Born in 1875, he was mainly active before the war, but left a giant legacy in both recordings and works. He is perhaps most famous for his cadenzas for this, the Beethoven concert. They survive in most versions of it you will find.
During the romantic age, the composer gave the opportunity to the performer to improvise a bit. This is called a cadenza. Classical music does not have that much opportunity to improvise, and as such performers are not used to doing this on their own. So they borrow. In this case from Fritz.
Kreisler also created pastiches of works by older composers like Vivaldi and Tartini. Nobody thought they were his, they were passed on as originals. When he revealed the fact in 1935, critics were outraged. He told them it didn’t matter, they already liked them, right? The name changes, the value remains. A good first step on the road to plagiarism.