I did a quick search for any design patents awarded to Marino Perna and found nothing. I checked for anything assigned to a company with Pantera in the name as well. Coddington has a few design patents on other wheels - not these.
Given that the design was essentially an upscaled replica of a wheel made in the late 60s/early 70s it is highly unlikely that it could be patented by Marino (at least not validly) - and any patents by Campagnolo would have long since expired.
Short answer, if there was anything stopping Coddington from making Marino's design for others it was likely a contractual arrangement of some sort - or Coddington just trying to be fair.