Datadog, if you read the link I posted you'll see that there are two types of NGO, DPI and eco/soc. Back in 1991 the criteria for
status was very different for the two types of NGO status.
The criteria for status as a dpi NGO changed quite some time after the jw's obtained status as an NGO in 1991.
I'd suggest that you write to teh UN itself to confirm this AND the dates of teh change in criteria.