You can customise your fetchxml
to have your requested result.
This should be something like this
<fetch mapping='logical'>
<entity name='account'>
<attribute name='name'/>
<link-entity name='appointment'
from='activityid'
to='accountid'
link-type='outer'/>
<filter type='or'>
<condition entityname='appointment'
attribute='activityid'
operator='null'/>
<filter type="and">
<condition entityname='appointment' attribute="actualend" operator="last-x-months" value="6" />
<condition entityname='appointment' attribute="statecode" operator="eq" value="1" />
</filter>
</filter>
I didn't tested but that give you what you asked, you can build a custom view with that or manipulate your gridview
.
Otherwise you could also use a report to give you this information.