There are essentially four episodes in which O'Brien tells the story of Setlik III, or gets it told for him. Put together, they must be describing at least two completely separate events if not more.
In "The Wounded", we learn that O'Brien, part of the crew of USS Rutledge under Captain Maxwell, was there exactly one day after a "squad" of Cardassian "militia" had made a "sneak raid" and wiped out "hundreds of civilians"; O'Brien grabbed a colonist's gun and, unaware of its setting, made his first-ever kill with that one. The dating is left unclear.
In "Tribunal", O'Brien is a veteran of a fight dated at 2362 where his Rutledge pal Boone gets caught by the Cardassians. He's almost immediately released but quits Starfleet (in fact he got replaced by a Cardassian agent), while O'Brien stays.
In "Paradise", O'Brien tells he saved a landing party at Setlik by fixing a field transporter, his first-ever involvement with transporters. Failure would have meant becoming POW. He saves 13 men and gets to wear gold and become the/a Tactical Officer on the Rutledge.
In "Empok Nor", Garak explains how O'Brien is "hero of Setlik III" for leading two dozen men against "Barrica encampent" and "taking out" an "entire regiment" of Cardassians. To this, O'Brien says he's not a soldier any more, but an engineer.
Since we further learn from "Realm of Fear" that O'Brien has worked on transporters for 22 years at that point, we have our two sets of data:
1) The First Setlik happens in 2347, in a prewar setting, and involves soldier O'Brien mopping up after a massacre conducted by a small Cardassian militia group, getting involved in a firefight where he makes his first-ever kill, and then having to flee and making his first-ever transporter repair. He remains a soldier, more specifically Tactical Officer (despite being enlisted) but now wears gold rather than whatever he wore before.
2) The Second Setlik happens in 2362, in the late stages of the war, and involves soldier O'Brien triumphing over large formations of regular Cardassian soldiers. Again, it's not a clear-cut victory as Boone gets captured, but it's a much more positive outcome than in First Setlik.
The two incidents could perhaps be blended in one by using a bit of semantic violence if not for the clear-cut dating issues: O'Brien must fiddle with transporters in 2347 already, but Boone can't get caught before 2362.
Nothing wrong with the setup as such. Apparently, Setlik III is a place worth fighting over, many times over (the original excuse of the Cardassian militia was that they thought Starfleet was using it as a staging post for attack), and Starfleet might well send skippers with local experience to fight over the place, many times over (Maxwell's family lived there until First Setlik).
Timo Saloniemi