It might make a little more sense distilled into this article, which I wrote for another blog afterward to discuss the matter.
Effectively, the original Maurice Leblanc Arsène Lupin stories borrowed Sherlock Holmes, much to Conan Doyle's annoyance. Subsequently, manga writer Monkey Punch based Lupin III on the Leblanc stories without permission, much to the Leblanc estate's later annoyance. (He was able to get away with it because Japan didn't honor trade copyrights at the time, and the Leblanc estate didn't even find out until years later.) Castle of Cagliostro drew on the Leblanc stories and the Lupin III franchise, and a number of other works, and inspired countless other works that borrowed from it in return.
And it never would have happened if the rights holders had been able to shut Leblanc and Monkey Punch down.