AlertObjects entries are not cleared when the alert is reset. You can still go from AlertHistory to AlertObjects to AlertConfigurations for alerts that no longer appear in AlertActive. I'll clarify this on the wiki page.
For example, if you have only one alert "Node is down" and only server "Crashy" that previously went down 10 times but is currently up, then you will have:
No rows in AlertActive
1 row in AlertObjects
10 rows in AlertHistory with EventType=0 ("Triggered") plus some other rows with other EventType values for when it was reset or acknowledged, etc.
The query you want should be straightforward to build.
Yep, I figured this out and posted replied on another post today that I mentioned this issue, just forgot to come back and update this post as well.