That Christ has been invisibly present since 1914 or 1918 or whatever, a date they pulled out of their hind ends!
What really gets me is their claim that Jehovah accepted the Bible Students as his cleansed organization in 1919, but they still believed all sorts of things then that Witnesses declare to be unscriptural now, including observing holidays, the cross, the Trinity, things they say are the beliefs of "false religion". They weren't even known by the designation of Jehovah's Witnesses then.
How does that work? Well, it doesn't.