Voronoi diagrams were first invented by Descartes, and then by Snow, and then by Dirichlet, before being invented by Voronoi.
The Koebe-Andreev-Thurston theorem relating circle packings to planar graphs was first proved by Koebe in 1936. Not knowing this result, Andreev re-proved it in 1970, and subsequently Thurston, who had proved it again, realized that his results followed from Andreev's work. All of this and more on circle packings is described here (PDF).
There are probably many other examples that establish the following meta-theorem.
To get a result named after you, be the last person to prove it.
A corollary might very well be:
To get a result named after you, publicize it everywhere.