What great memories! Those Christmas ornaments were put up one Christmas, and then Don liked them so much that he left them! Your recollection of 106th St is correct; it's now Duke Ellington Blvd, I think. Don lived there some thirty years, and, while he lived there, he made some adjustments to his apartment. Someone bought the building, and is now suing Don's estate about the changes, so we can't even retrieve family mementos! You'll recall from seeing the apt that it was quite a nice place for an NYC apt.
As a kid, I used to design Christmas cards just to send to Don.