We bought North American publication rights, and copyrighted the material to DGP. We could take the material, print it and reprint it all we wanted, using it over and over in future products marketed to North America if we wished.
We often, as a courtesy to the author, paid them for a second printing as well when we did it (rare), but mostly just a token fee compared to what they got the first time it was published.
Which means the authors can freely publish their material outside the US and sell it to non-US markets if they wish. Now this gets a bit tricky because publishing the articles over the internet is *global* which includes North America, and is an infrigement on DGP's rights -- which today is Roger Sanger.
The MTJs were copyright GDW because using the Journal name on a Traveller magazine was GDW's property and they would only let us publish under that name if we copyrighted the material to them. So GDW, now Marc Miller, owns that content.