Earlier quoted context omitted.
That said, isn't it the case that one can't just take something that exists in common usage and trademark it as-is? For example, the basic structure of the fairy tale about Aladdin and the magic lamp had been around for a long time, and was clearly not originated by Disney. Consequently, Disney has no right to claim trademark or copyright control over the name Aladdin or or anything generally related to the story. Th…
Was "space marine" in common usage in 1987, though? The fact that it exists in a long out-of-print pulp novel doesn't mean that everyone understood its meaning. Again, this isn't a patent. All that's required is that, when the trademark was registered, GW's usage of the term was unique and relevant to their business.
I would say it was in common usage.