Read this last week, even though he won as a King I will always see him as a Flame. Nice move on Calgary to have him retire as a Flame, nothing but good things to say about the guy. He filled a need and help the Kings win.
I remember seeing him in 2004 on the way to the Cup Finals and he was a beast.
His last NHL game as a player was with the Kings, but I don't think he officially retired at the end of that season.
His contract expired, he informed the Kings he had no intention of playing with them (or anyone) again and stopped. The key is the retirement paperwork, and while we don't know when he filed it, from a legal POV I don't think he did because he signed a 1 day contract with the Flames and to the best of my knowledge with any players union when you file your retirement paperwork, that's when it's official.
That tells me he did not file after he left LA and probably had spoken with the Flames at some point hammering out details of "Robyn Regehr Night", where he would be honored by the Flames. But in order to have CALGARY FLAMES listed as his last formal NHL team he needed to sign a contract for it to be binding and legal and filing retirement would not have allowed that, that would have indeed had LOS ANGELES KINGS list as his "retirement" team.
It's all ceremonial but technically...Big Rig retired a Flame.