Of course they have, they would have to do a lot of work with their new URLs to be even close to as successful as they were before. It's absolutely fundamental

Of course they have, they would have to do a lot of work with their new URLs to be even close to as successful as they were before. It's absolutely fundamental to keep the same URLs when you are trying to beat the absolutely best at SEO (They are beating people like MDN, made by freaking Mozilla, after all)