Ridvan - If this is such an important event; why are different years given on this?

Baha'u'llah

The date of Baha'u'llah's declaration is fixed by Nabil, the follower of Baha in his chronological poem. He says the claim was made when Baha was fifty years old, which would be A. D. 1866-67 (Journal Royal Asiatic Society, 1889, pp. 983-990). Mirza Abu'l-Fazl, the famous Baha'i missionary, confirms this date, in his Istidlaliyya (Journal Royal Asiatic Society, October, 1892, p. 703, note 1).

'Abdu'l-Baha, in his Traveller's Narrative, in his effort to make it appear that Baha had been the leading figure in the Babi Movement from an earlier time, "deliberately and purposely antedated the Manifestation," says Dr. Browne, stating that this important declaration was made by Baha in Baghdad in A. D. 1852, fourteen years earlier than it actually occurred!

The modern Baha'is have fixed the date as April 21, 1863, - which is only three or four years too early (Baha'u'llah and the New Era, Esslemont, p. 36.) See also Journal Royal Asiatic Society, April, 1892, pp. 304-306.