Proven is better used as an adjective. He has proved his point. He has a proven record of achievement. Recur , more widely used than reoccur , implies the repetition more than once of an event or experience, sometimes according to a definite pattern. Reoccur suggests a one-time repetition.
Corresponding nouns are recurrence and reoccurrence .
Recurrence is much more widely used. These that clauses do not require a comma. Of all my typewriters, the typewriter that is on my desk is the best. Which is best used to introduce a clause containing incidental or nonessential information. These which clauses require commas.