The only (intel) Thelio Mira listed under previous models is the b1: https://tech-docs.system76.com/models/thelio-mira-b1.0/README.html
The most recent (intel) Thelio Mira is the b4-n3: https://tech-docs.system76.com/models/thelio-mira-b4-n3/README.html

So it looks like at least the docs for thelio-mira-b3-0 are missing, if not other models (idk what others might exist).