The First Vision
There are four different versions of the First Vision: 1832, 1835, 1838 (official version), and 1842.
Altogether there are even ten different versions of the first vision. Written either by Joseph Smith himself or by others.
Gordon B. Hinckley, former President of the Mormon Church, made the following statement regarding the firstVision:
"All our strength rests in the validity of that vision... It either happened or it didn't. If it didn't happen, then this work is a fraud. If it happened, then it's the most wonderful and important work under heaven. " (Fall 2002 Conference)
For a long time only one version of Joseph Smith's First Vision in 1820 was known within and outside the Church. Today, this can be found in the “Pearl of Great Price”.
The official version in the history of the church dates from 1838 and speaks of a faith awakening with missionaries of all denominations, which drew the young Joseph's attention to the diversity of religions. Smith goes on to say that he was criticized and persecuted for his decision not to join a church and had another vision three years later. In it he would have been informed of the discovery of golden plates engraved with written revelations. This version has been criticized because a faith awakening for the region has been proven from earlier years and the year 1824, but not for 1820. In addition, contrary to his statements, the rejection of all churches cannot have had any particular influence on Smith's family, since his mother and others relatives were still active Presbyterians many years later, and there is evidence that he himself attended a course of the Presbyterian Church several years after the official date of the First Vision.
Wesley P. Walters: New Light on Joseph Smith's First Vision, 2008. From the Institute of Religious Research - Project Mormons in Transition website
Other versions, some of which deviate considerably from this, survive from the years 1827 and 1830, although they were not published until much later as memoirs by family members and early chroniclers of Smith. The first draft from Smith's own hand dates from 1832 and was only published in 1965: Here the vision occurred in 1821 (Smith was already 15), he had been reading the Bible for years and was for himself to the Concluded that all denominations had deviated from true Christianity. Only Jesus Christ appeared to him here and forgave his sins. There is no talk of a revelation about the truth of the denominations. The second vision with the announcement of the golden plates therefore took place two years later.
In 1859, a temporary close companion of Smith's reported his reminiscences in an interview. According to this, the vision would not have taken place until 1827 (Smith was then 21 years old) and it would have been related to the treasure hunt that would also have led Smith to the gold plates. This version agrees almost entirely with the earliest reports cited above.
First Vision versions follow: Institute of Religious Research - Project Mormons in Transition: Joseph Smith's Changing First Vision Accounts
Institute of Religious Research - Project Mormons in Transition: 1832 First Vision Account, with digitized copy and transcription of this version
Institute of Religious Research - Project Mormons in Transition: 1859 First Vision Account by Martin Harris
Why is there no specific First Vision date?
There are four different versions of the First Vision: 1832, 1835, 1838 (official version), 1842
Altogether there are even ten different versions of the First Vision. Written either by Joseph Smith himself or by others.
No one, including Joseph Smith's family and members, ever heard of the First Vision until twelve to twenty years later. The first and earliest written account of Joseph Smith's First Vision was 12 years after the springrecorded from 1820. There is absolutely no record of the First Vision before 1832.
In 1965 an account of Joseph Smith's First Vision was published. This account dates from 1832 and is the only handwritten one by Joseph Smith. There it says:
“...I cried out to the Lord for mercy, for there was no one else to turn to and obtain mercy, and the Lord heard my cries in the wilderness, and while I was thus crying out to the Lord in my 16th year, came from above a pillar of light brighter than the midday sun and rested on me and I was filled with the Spirit of God and the Lord opened the heavens to me and I saw the Lord and he spoke to me and said Joseph my son. Your sins are forgiven you, go your way, walk in my law and keep my commandments. Verily I am the Lord of glory, I was crucified for the world, that all who believe on my name may have eternal life. Behold, the world is in sin now and not one is doing good, they have turned from the gospel and do not keep my commandments, they approach me with their lips, but their hearts are far from me, and my anger is against the inhabitants of the earth ardent, I will visit them for their ungodliness and bring about what I have spoken through the mouths of the prophets and apostles. Verily I come swiftly, as it is written of me, in a cloud enshrouded in the glory of my Father. And my soul was filled with love and for many days I could rejoice with great joy and the Lord was with me. But I could not find anyone who would believe the heavenly vision..."
http://en.wikipedia.org/wiki/First_Vision#1832_Smith_account (translated from English)