I am fairly certain reading an article that reviewed one of the first shows Bon Jovi played together post Jersey Syndicate Tour where Jon came out and played Santa Fe by himself on the Piano, and then was joined by the rest on With A Little Help From My Friends. I don't remember which magazine it was. I would guess Metal Edge or Circus. Metal Edge was the most detailed regarding that kind of info back then.

I guess it boils down to someone having the article in question who can identify the supposed show and someone who was there to verify it.