Joseph Smith's own accounts of the first vision must be viewed with some reservations. No mention of his “First Vision” “”which supposedly took place in 1820″”was ever made in print, until twenty years later when Orson Pratt, a longtime friend of Joseph Smith, published an account of the vision in a book called Remarkable Visions. Then in 1842 Joseph himself published an account of the two gods who appeared to him in a grove and told him not to join any existing church.
Why no hint of any kind concerning this first vision is found in any Mormon (or non-Mormon) literature published prior to 1840, I cannot understand. After all, this was supposedly a major event in human history! By comparison, look at the way that Peter and John were absolutely irrepressible in speaking about their experiences with a risen Savior. Even the threats of powerful officials had no effect on them, and they said, “For we cannot help speaking about what we have seen and heard” (Acts 4:20.)

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.