Nike’s Apple Watch integration used to be referred to as Nike plus. And they used the + sign to indicate that. ( it goes all the way back to 2006ish and stood for Nike + iPod) At some point, it was renamed to Nike run club. And I believe that is when they dropped the + from the packaging. There haven’t been any features removed from the Apple Watch corresponding to the name change.
There were some changes (removal of the website, etc) but none of those were related to features offered on the watch.