I think we need give example.
Something like this:
Please note that these restrictions are per Registered domain - they do not apply to servers or different domains - only to the domain and its subdomains.
So, for example, if you have domain.com and domain2.com you can register 20 certificates per week for each of these domains.
Another way is to add it FAQ.
I have 30 1st level domains can I generate the certificate for them at once?
Yes, you can we restrictions are per Registered domain, they apply to each domain individually.
Now I see that the answer is pretty obvious, but I think if we do it it can really help new people a lot.