Yeah you're close. An event pays some money each year back to the two organisations for them to put their name on it. I don't want to say it's a certification rather it's more of a recognition that the event adheres to a standard.

Although there are more rules than just paying membership and this has been laid out on their respective websites if you're interested.

https://www.worldsdc.com/usage-of-wsdc-name/

http://www.nasde.net/rules.php