In the latest episode 'The Lighthouse' the Jack which is living in the timeline where flight 815 didn't crash finds that he had his appendix taken out when he was very young, although he does not remember this.
This scene gave me the impression that there is some sort of bleeding effect between the two timelines. It seems that that scar should not be there but has somehow bled from the old timeline into this new one. And the timeline has a way of course correcting itself with Jack's Mother claiming that he had it as a child, and Jack sort of remembering the incident.
