That would be pretty awesome, but it's not how I interpret the following: "This limit measures certificates issued for a given combination of Public Suffix + Domain (a 'registered domain')."

Do you have a source?

I do not believe this is true. That rate limit applies to second-level domains and all subdomains.

This is not true. I know from experience.

See the first point in https://community.letsencrypt.org/t/rate-limits-for-lets-enc...