According to the MoD, Harry has been in Afghanistan for 10 weeks - which (according to my maths) means he went before Christmas).
Now, I can't remember what the BBC and other news organisations said when covering the Royals going to church at Christmas, but I'd be interested to know what they said, if anything, about Harry not being there.
As I understand it, the news organisations knew that he had gone but accepted the request not to report this.
Fair enough to many people's minds. But I bet the public wouldn't be so understanding if they thought that had been positively lied to.