Even if the site is using a "popular" CDN, which does it use? Google? JSDeliver? Cloudflare? Unpkg? Which specific library and which of its versions? There are

Even if the site is using a "popular" CDN, which does it use? Google? JSDeliver? Cloudflare? Unpkg? Which specific library and which of its versions? There are too many CDNs and library versions to carry the advantage of caching across different sites.