Arrgh. AGAIN: it's not a patent! "Prior art" proves nothing. If this figure's manufacturer was not a going business venture in 1987 (or whenever GW filed that trademark) then GW was entirely within their rights to file such a trademark.
And even if this was 100% contemporaneous, the party with standing to challenge that trademark would be the toy company, and not the linked post. The remedy would be to immunize the toy company from GW, or perhaps to award them damages due to GW's mark causing loss of sales.
He's not claiming that their trademark is invalid because of "prior art", he is saying that they should not have a trademark on the term in the same way that Tropicana should not be permitted to have a trademark on "orange juice".
That is to say, "space marine" and "orange juice" are both clearly descriptive marks. That "space marine" is a descriptive mark is evidenced by it's long history of usage.
The article says GW is claiming an implicit or common law trademark rather than a registered one. The rules for that are far more grounded in equity than the rule based statutory system.
Edit: that is to say the expansion into the book market is a common law extension. To be clear the mark was registered in the game market.
And even if this was 100% contemporaneous, the party with standing to challenge that trademark would be the toy company, and not the linked post. The remedy would be to immunize the toy company from GW, or perhaps to award them damages due to GW's mark causing loss of sales.