Watching Cm Waters's "Episodic Christmas" makes me wonder, are there any long-running tv shows (4 seasons or more) that never had a Christmas episode? The A-Team is the first one that comes to mind.
I'm almost certain that there was a Christmas episode of the A-Team. I think that I remember Hannibal dressing up like Santa.
There was also an episode in the fourth season "Uncle Buckle Up" where Hannibal played the costumed sidekick of a popular kids show host that was being shaken down by the mob.
It wasn't a pure Christmas episode in that no one dressed up as Santa or anything like that. But it did take place during the Holidays, and the battle at the end of the episode was a homage to "Babes in Toyland"
Lost never had a Christmas episode over six seasons. The closest they may have come was The Constant, but that aired in February, I believe. Part of the main action just happened to take place on Christmas Eve.