[@PapiTan]
Their persona should be new, at least. I have some flexibility with them having been an intermediate-level Hero before but then needing to swap to a new identity/hero form for whatever reason.

And this current situation, specifically of Neo-Astraea and corpo-heroes with a big fanservice presence, has been going on for about 50 years. History taught in school also only goes back to around 50 years (outside of vague "we founded this city in the far past" kinda hijinks). There are proper legends of pre-AE Heroes though, like...

The Firewatcher
The Rust Saint
The Imaginary Idol
Old John
The Ivory Hero.

Though at this point, there's dozens of unverified stories about them so you can make up whatever you want.