Between about 364 and 370 CE, a visionary named Yang Xi reported a series of nocturnal visitations from beings he described as perfected immortals, figures who had already completed the journey to transcendence and now occupied a celestial hierarchy considerably higher, in the visions' own account, than the deities recognized by the Daoist schools already established at the time. Yang Xi recorded what these visitors told him, instructions on meditation technique, alchemical practice and the structure of the heavens the soul would need to ascend through, and those records circulated among a small circle for generations after his death.
Tao Hongjing did not witness any of this directly. Born in 456, roughly a century after Yang Xi's reported revelations and living until 536, he inherited scattered manuscripts descended from that original material, worked to establish which fragments genuinely traced back to Yang Xi, arranged them into a coherent structure, and added his own extensive commentary explaining and defending their authenticity to skeptical contemporaries who had reason to doubt manuscripts that old.
The resulting compilation, Zhen'gao, is therefore neither a first person account nor a disinterested scholarly edition, but something in between, a later editor's considered reconstruction of an earlier visionary experience, shaped as much by Tao Hongjing's own century as by Yang Xi's, which is exactly why Shangqing practitioners have long treated the compiler's editorial judgment as inseparable from the revelation itself.