Rolex SA, one of the world's best known luxury brands and a constant target of cheaper knock-offs, has an obvious interest in protecting its IP. So when Polo Ralph Lauren applied to register various trademarks that included “RLX,” Rolex quickly opposed the applications on the grounds that the marks could confuse consumers.

Siding with Ralph Lauren, the U.S. Patent and Trademark Office rejected the last of those challenges in 2012, paving the way for the company to potentially sell RLX-branded watches under its Ralph Lauren Extreme line. In a ruling made public on Monday, however, a federal judge in Manhattan refused to throw out a follow-on lawsuit brought by Rolex later the same year, keeping Ralph Lauren and its attorneys at Greenberg Traurig on the defensive.

U.S. District Judge Thomas Griesa ruled that Rolex, represented by King & Spalding, can press ahead with claims that the PTO's Trademark Trial and Appeal Board improperly dismissed its challenge to the trademarks “RPX Ralph Lauren” and “Ralph Lauren RPX.” The judge declined to grant summary judgment to either side in the case, finding that neither had established conclusively whether Ralph Lauren intended to commercialize the marks at the time of the original applications.