As I recall Mike Lull and several other builders were targeted by Gibson, it went to court, and they (Gibson) actually had no rights as at least at that point they hadn't copyrighted the shapes.
Gisbo contacted me around two years ago claiming rights. I never answered, just removed stuff. They sent me another letter a few months later saying they were dropping the matter...again, which I never answered.
The docs Gisbo sent me showed Reverse, NR, and Explorer shapes they were claiming trademark on as well as their Thunderbird logo. After I scrubbed that stuff they came after the ThunderBucker logo.
Hamer has just been rebooted and their Standard would definitely be in violation of any Explorer copyright.
Of course, lawyers have been known to claim things that aren't actually true to get what they want...the law usually being what the party with the deepest pockets says it is.