macOS / Calendar / search the past

I have 5 Macs (Mac Pro, 2 MacMinis, 2 MacBook Pros) all at High Sierra, all logged in identically to the same Apple ID and the same Calendar & iCloud preferences. iCloud settings are identical.

All events, going back several years, are present on the calendars of all five Macs; and yet when I search for a past event on two of them, the events aren't found (e.g. kidney), whereas, on the other 3, the search finds the events.

This is not a single event issue: it is all events more than a couple of months old. The events are there, and can be found by search on three Macs, but not on two other. Naturally, the Mac with the issue, is my primary desktop. It is critical that I get the full search function on my main Mac.

What needs to change on the two 'problematic' Macs?

Thanks, Brian