I am sorry, I do not care what you dig up on the Web that contradicts this … BUT there was NO Dean of the College of Cardinals prior to 1150.
A very straightforward reason for this. There was NO College of Cardinals prior to 1150. So you couldn’t have a Dean of an institution that wasn’t in existence.
People get confused about this and I can empathize. Most assume that there has always been a College since the notion of cardinals came to be. [Then again, I had MD from Canada, who, yesterday, got very confused between conclaves and consistories!]
Please check out this post at popes and papacy for more information on this topic.