“Making these types of changes, where you go from 5 million URLs in Googles index to 500,000 URLs in Googles index can make a substantial distinction for your site in Google Search. It is not like you are missing out of 4.5 million pages, because all of those pages are replicate 50 times to the 500,000 URLs. It simply makes things cleaner and more constant for Google and it helps combine signals to the primary product or category page URL.So when you discover these URL duplication issues, talk to your advancement group about how you can just serve the canonical URL to users and Google.