[anbu32]

GHK published their paper later in the year (although they apparently arrived at the result independently..), which might be why they were left out.

In 1962 P.W. Anderson worked out that Nambu–Goldstone massless mode can combine with the massless gauge field modes to produce a massive vector field (e.g. the so-called "higgs-mechanism", but in a non-relativistic context). In 1964 E&B,H,GHK showed that this is also possible in a relativistically invariant theory.

Here's a twitter comment from John Preskill (caltech): "The emphasis on finding a relativistic model may be misplaced, though. Anderson understood the mechanism well." https://twitter.com/preskill/status/387580651664191488

So maybe Anderson is more deserving of the last spot than GHK.