Truth be told, I've lost track of Shadowrun's in-game "future history" when 3rd edition came out, which we've never got around to play. However, I do know (thanks to various gaming blogs, etc.) that the metaplot has steadily advanced through the subsequent editions.
Now that 5th edition is out, our group is contemplating giving Shadowrun a new try, and I wonder whether the history of the world of the game has been evolving and emerging continuously since 2nd ed., or if there's been some major retcons along the way.
For bonus points (:)), have any new major revelations been made concerning the link between Earthdawn (whichever edition) and Shadowrun? (If they're too numerous to list: Where should we look for a comprehensive list?)
Edit, to answer @Scrollmaster's question: The more detail you provide, the better. However, if no one comes up with a detailed list, even a "There have been no major retcons at all" or a "Xth edition seriously retconned X-1th edition concerning important dates and dragons" (that is, a 3 lines long answer) will also suffice. :) (Sorry, I can't really list my points of interest since I don't remember 2nd ed. too well and I haven't really read 5th edition yet.)