Not that it will help you figure out what happened, but...
Have you tried deleting one that you know should show up and re-entering it? If it then shows up, you have a work-around, but no answer.
I just tried a search on something that repeats every month, and has no end date specified. It was found from August 2008 to November 2011. So, there are limits to the search function. I don't know where to find them. Didn't see anything in Preferences.
This appears to affect only one of several calendars I maintain in iCal. When I search for a keyword, I get results only up through June ?09. Have tried deleting iCal-related prefs in home library. Have run Disk Utility thrice.
Many thanks for any suggestions offered...