Oubliette has hit the nail squarely on the head – I would just like to add;
- Pure Chance – when another religion predicts something that does come true.
- True Prophecy – when the WTBTS predicts something that does come true.
Not that there is a single example of the latter, but it is why you will find the Watchtower making statements such as this;
"Today, Jehovah’s Witnesses point to the sign given by Jesus and look back upon 1914 as the year when his invisible presence in Kingdom power became a reality. But how could they have had advance knowledge of such a momentous event? Not because of extraordinary human wisdom. No, but because they have prayerfully studied the Scriptures, heeded God’s prophetic word and paid more than usual attention to what God’s Son foretold." (The Watchtower, April 1, 1984, page 16).
Of course this is bullshit because prior to 1914 they believed Christ’s invisible presence started in 1874, but that’s another subject altogether.