Why would Steve Jobs be freaking in 1981 when he already saw it back in 1979?

http://en.wikipedia.org/wiki/Xerox_Star

Also Folklore.Org says the same thing: http://folklore.org/StoryView.py?project=Macintosh&story...

"This is obviously the biggest single jump in the entire set of photographs, and the place where I most wish that Bill had dated them. It's tempting to say that the change was caused by the famous Xerox PARC visit, which took place in mid-December 1979, but Bill thinks that the windows predated that, although he can't say for sure."