Re: Was Dax Sisko's XO circa 2374 ?
I'm sure certain episodes inferred that O'Brien had a failry High Security clearence level.
The problem with O'Brien is they ret-conned him to be a NCO. I'm sure that if they realised that they were going to use O'Brien as much as they did during TNG's run they would have given his character some more fore-thought. Remember prior to moving to DSN he had appeared in something like 40% off all TNG episodes.
On the continent of wild endeavour in the mountains of solace and solitude there stood the citadel of the time lords, the oldest and most mighty race in the universe looking down on the galaxies below sworn never to interfere only to watch.