You can have thousands of domains with SSL certs, that doesn’t mean they all need to be on a single certificate. Hence my question of what was the reason / need for over 100 domains on a single certificate ? it’s generally not good practice and slow (for users connecting) if you have a large number of SANS on a single certificate.
I don’t understand your question fully.
Normally, on a single server there will be lots of domains. Let’s say it’s a server with 200 domains. There will be domain1.com which has associated subdommains www.domain1.com, mail.domain1.com, forum.domain1.com and there will also be domain2.com which also has www.domains2.com etc.
You can have a single certificate which is for domain1.com, www.domain1.com, mail.domain1.com, forum.domain1.com
A second certificate would be for domain2.com and www.domain2.com
You configure the server ( via apache, nginx or whatever your webserver is ) to use the correct certificate for the domain.
Hence my question - What is the reason / need for over 100 domains in a single certificate ?