Production code column 

There are a couple of production codes listed on the article, but these are completely incorrect. The Doctor, the Widow and the Wardrobe had the production code "X11" not "7X". Additionally, production codes were scrapped after that episode was produced, so episode 1 was definitely not "7.1". You will never find any official source confirming this as the code, I am aware of one encyclopedia that used this as a code, but as somebody connected to the production team (Edward Russell I believe) confirmed on Twitter, this was purely for the sake of consistency across the episodes, indeed they also got all the codes for the 2010 and 2011 series wrong just to avoid duplication of the RTD era codes.