Hey antdude,
Calendar search would only be expected to locate events up to 1 year in the past. You can find more information on searching on your iPhone here: Use Search on your iPhone, iPad, or iPod touch
"Change search settings
You can change the search settings to limit which apps and results appear while you're searching. Here's how:
- Go to Settings and tap Siri & Search.
- Scroll down and select an app.
- Then select Show App in Search, Show Content in Search, Show on Home Screen, Suggest App, or Suggest Notifications.
To turn off Siri Suggestions for all apps, go to Settings > Siri & Search, and turn off the settings you want."
Thanks!