When I search with the following JQL:
project = 'ABC' and issuetype = 'epic'
It does not return all the epics under the project. In fact, it fails to return quite a lot of them. Could not find a reason based on epic status.
JIRA search in general sucks - reason I was trying the above was because simply searching for the title of the epic failed, coming back with "no issues were found to match your search"