Little info from Levi page - hope it helps!
Everyone who has worn Levi’s® 501® original jeans contributed to their ever-changing story, and this season brings a first: limited edition Celebration 501® jeans featuring exclusive gold-plated buttons and Levi’s® proprietary selvedge.
“We recently discovered a pair of deadstock 1947 501® jeans, meaning that they’ve never been worn. Any denim aficionado will recognize the 47’s as ‘grail jeans’ and to find a pair in headstock condition is unbelievable,” Jonathan said. “What we found was that the buttons on this special pair had oxidized to a gold color – so we replicated the golden hue for this limited edition.”