This inter-link is referred to in the United Nations article

This is the DPI/NGO Directory from 1997, which was published in the middle of the Watchtower Society's decade-long membership as an NGO registered with the Department of Public Information associated with the United Nations. All NGO members were given this directory, including the Watchtower Society.

Note that this next scan, on page V of the introduction, it is openly stated that "NGOs associated with DPI disseminate information about the United Nations to their membership, thereby building knowledge of and support for the Organization at the grassroots level. This dissemination includes (Heading: How do NGOs and DPI Cooperate?):

• Publicizing UN activities around the world on such issues as peace and security, economic and social development, human rights, humanitarian affairs, and international law.
• Promoting UN observances and international years established by the General Assembly to focus world attention on important issues facing humanity.

The very next page, page VI, continues on to state reiterate the criteria for NGOs associated with DPI. Note that eligibility requires the following of the NGOs:

• Share the ideals of the UN Charter
  
• Operate solely on a not-for-profit basis
• Have a demonstrated interest in United Nations issues and proven ability to reach large or specialized audiences, such as educators, media representatives, policy makers, and the business community
• Have the commitment and the means to conduct effective information programmes about UN activities by publishing newsletters, bulletins, and pamphlets, organizing conferences, seminars, and round tables, and enlisting the cooperation of the media.

Since all NGOs associated with the DPI recieved this very same directory, with this very same recap of criteria each year, the Watchtower Society cannot truthfully claim ignorance of the criteria during their time of membership.