When did O'Brien lose his commission?

[C.E. Evans]

Given that Starfleet apparently didn't have any real enlisted insignia until late well into DS9's run, those two pips O'Brien wore could have meant anything, including "Transporter Chief First Class", IMO...

 

[The Wormhole]

O'Brien identified himself as an NCO to the Rozhenkos, so if he was moonlighting as an officer he had given it up by Family.

Indeed, Mr Rozhenko even recognizes O'Brien as a Chief Petty Officer, despite the Lt. pips on his collar.

 

[RandyS]

Before he married Keiko, Miles could never find his clean uniforms. So, he simply threw on any one he could find as long as it was the same color. The rank pips actually belonged to whoever he borrowed the uniform from.

 

[Timo]

Indeed, Mr Rozhenko even recognizes O'Brien as a Chief Petty Officer, despite the Lt. pips on his collar.

"Correction: By the pips on his collar."
"Thank you, Data."
"A common mistake, Sir."

Timo Saloniemi