I'm sure the vast majority dont know about it. I certainly didn't when i was in. I get the following response whenever i bring this up:
1. If I'm not holding a copy of the UN letter - they deny it and say it'll be an apostate lie and "i cant believe you were taken in by it"
2. If i am holding it - they deny it and say it's an apostate lie and "i cant believe you were taken in by it"
3. If i show them the letter and Watchtowers reply about it only being so they could access the library they say "they're imperfect men, they make mistakes, doesn't that show you how humble they are?"