You need to add a ServerName directive to the <VirtualHost> config for each virtual host you want named. For example, the below will configure 3 named virtual hosts on ports 81, 80, and 6969:
<VirtualHost *:81>
ServerAdmin sysadmin@virtual1.domain.tld
ServerName virtual1.domain.tld
DocumentRoot D:/HTTP/virtual1
ScriptAlias /cgi-bin/ "D:/HTTP/virtual1/cgi-bin/"
</VirtualHost>
<VirtualHost *>
ServerAdmin sysadmin@virtual2.domain.tld
ServerName virtual2.domain.tld
DocumentRoot D:/HTTP/virtual2
ScriptAlias /cgi-bin/ "D:/HTTP/virtual2/cgi-bin/"
</VirtualHost>
<VirtualHost *:6969>
ServerAdmin sysadmin@virtual3.domain.tld
ServerName virtual2.domain.tld
DocumentRoot D:/HTTP/virtual3
ScriptAlias /cgi-bin/ "D:/HTTP/virtual3/cgi-bin/"
</VirtualHost>
HTH.
-geoff