SPRINGFIELD – In 2007, Springfield’s gleaming new shrine to Abraham Lincoln was open, but it lacked touchstone pieces to show off, so organizers paid $6.5 million for the most symbolic Lincoln artifact available: one of the 16th president’s stovepipe hats. A dozen years and as many studies and hand-wringing public statements later, there’s no concrete evidence that the felted beaver-fur hat ever sat atop Lincoln’s 6-foot-4 frame. Has anyone requested a refund? No, and it doesn’t appear anyone will soon.