Suppose, a server hosts

   https://www.master.com/

and thus is equipped with a (single domain) SSL certificate.

Furthermore, suppose there are some web apps below master.com:

   http://wiki.master.com/
   http://docs.master.com/
   http://cal.master.com/
   ...

To protect those web apps, one could use a wildcard certificate for master.com, which reaches 1 level down. This wildcard SSL certificate would thus protect connections to each of these web apps.

Question: Could this wildcard certificate be issued, although another (non-wildcard) certificate for www.master.com has already been issued?

Do CAs exchange data to ensure, that the domains of issued certificates do not overlap?