WT writers of specific UN articles do not seem to be in 'sync' with other WT writers that mention the UN on other articles.
The 'other ariticles' writers may not even know about the NGO/UN association.
It is like the WT publication about the bible book of James published over two decades ago. It was a totally different type of publication, as far as content. Much later I got an idea about who wrote it, no wonder.
About the FCCC, the WT has always quoted basically the same, out of context, portion you mention I have read such a quotation a thousand times from the WT, they really like it.
In my opinion this UN issue is very important, the WT has said so much about the UN. I used to be a "book study" conductor using the book that explained all the UN "revelation". I think it was titled "babylon the grape..." it was a red book by the way.
Most jw did not understood the book, there are three (3) beast mentioned with 'seven head' each, 21 heads and 30 horns to talk about, not to mention other animals here and there. hehehe
Like I said before just quoting or displaying WT and UN documents plus some individual experiences with the WT should do the job.