Turns out, mom spotted another bookcase that day. The house across the street from her hairdresser was also having a yard sale. This lady had this mammoth bookcase, a true bookcase, one that will hold heavy art books and the like. Someone (her husband, perhaps?) had made this thing, and it is very heavy, very sturdy, and has nice finishing details like trim on the front of the shelves and crown molding on the top.
It has now taken up permanent residence in Oliver's room, where it almost completely fills the end wall. Seriously, there's only about 6" on either side. It looks like it was made to fit that spot.