Nabil Zarandi's history (The Dawn-Breakers) is partisan, hagiographic, and frequently mistaken about dates and other vital details.

A further difficulty with Zarandi's text lies in the rather late date of its composition. The author, originally known as Mullá Muḥammad and later as Nabíl-i Zarandí or Nabíl-i A'zam, was born in the village of Zarand on 18 Şafar 1247/29 July 1831. He himself states that he became a Bábí in 1265/1848-49.684 His history of the sect up to 1853 was begun in 1888 and finished in 1890; the sequel was written between then and his death in 1892. This means that there was a time-lag of something between thirty-five and thirty-seven years between the latest events described in the narrative and the time of writing, with as much as ninety-five between then and the earliest events recorded. If we bear in mind that Zarandí was not a professional historian working with a large range of reliable documents and that the normal distortions of hindsight were, in his case, much exacerbated by numerous shifts in doctrine and attitudes towards individuals, this time factor becomes extremely important. And it must not be forgotten that Zarandí's history, like those of Mírzá Jání and Hamadání before him, is partisan, hagiographic, and frequently mistaken about dates and other vital details.

(The sources for early Bábí doctrine and history A survey by Denis MacEoin)

https://bahai-library.com/pdf/m/maceoin_sources_babi_history_proofed.pdf