MadalinStroe: I don't know anything about US trademark law, but I think RWarehall is right, that sounds like legalese, and shouldn't be taken out of that context. It's just a term, used to simplify the understanding of the complaint, by the legal professionals.
I have no idea who is right and who is mistaken, but this is affecting both projects, which is sad.
Hmm, perhaps it is legalese. I think the more important thing is the technicalities of the 1988 agreement. It clearly contains clauses which cause rights to revert to Fred and Paul, so my guess is that the case(s) will hinge on whether those bits came into effect or not.
Certainly, the events of 2011 seem to suggest they have a case, where the old games were released on GOG by Atari but then 'republished' here by Fred and Paul after Atari agreed they didn't have the (sole?) rights. I imagine correspondence from that will be important evidence.