Like the other thread about the Tilted Kilt, it seems to me that this has been opened in the wrong forum, and should rather be in The Tartan Place.
Personally I feel that the SRT has made a major boob here in registering something so similar not merely to another well-known tartan but probably the best-known tartan in the world.
I don’t know what criteria are used to define “sufficient difference”, but it seems to me that the rules are not yet clear enough.
Regards,
Mike