This statement is not true. Participants in the PCUSA Board of Pensions are fully vested after three years. That means that most pastors vest during seminary. The Board of Pensions is actually one of the bodies related to the PCUSA that is not monkeying around - at least on the Pension side of things. See: http://www.layman.org/wp-content/uploads/2013/02/pension-brochure.pdf
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A pastor told me that.