You got it right. You can have multiple SSL certs for an IP Address, but only 1 SSL certificate per port on that IP Address. That is why only one cert can be associated with 443. A certificate authority such as VeriSign has to tie the certificate to something. The server's IP address is like it's phone number. When I use a certificate for
Free Web Space and Site Hosting it resolves to the IP address. The server then decides which port to use with the certificate. The Certificate Authority doesn't care if you run the SSL cert on 443 or another port as long as it's on the right IP address.
This link has a lot of info on IIS and SSL.
http://www.microsoft.com/technet/pro...ty/c06iis.mspx