>references to Purim do not feature in the Jewish literature before the 1st century CE.
> the festival had long been established by the 2nd century CE as evidenced in the tractate Megilah of the Mishnah (corpus of the oral tradition of Jewish law).
For a contemporary example, Christmas trees do not feature in English or American Christmas traditions before the 19th century, but were long established by the 20th century. Ditto white wedding dresses.
(The rise of of both traditions dates back to Queen Victoria.)
It's perfectly consistent with it being established in, say, the early 1st century CE and spreading rapidly; a century is plenty long enough for a festival to be "long established", which it was (per the quote) by the second century CE, despite being absent from the literature before the 1st century CE.
> the festival had long been established by the 2nd century CE as evidenced in the tractate Megilah of the Mishnah (corpus of the oral tradition of Jewish law).
I'm confused by this.