The book was written in 1978 and so only covers historical occurrences that happened up to that date.

Over the last century seven historical occurrences were known to exist.

The novel has substantial basis in historical occurrence.

There are many historical occurrences that are gone today.

There are 83 historical occurrences, and plants were located at 43% of the sites in recently surveyed.

The ballad is often supposed to be based on a historical occurrence, but no such event has been located that matches it.

This may be an allegory for some historical occurrence, in which one group forced another out for a perceived fault or slight.

Wasn't this merely a literary device to stress the significance of the Crucifixion, and not a reference to an actual historical occurrence?

Most historical occurrences are now extirpated and the plant has not been collected since 1967.

There are many more historical occurrences which no longer exist.