It can take years for crawling on migrated domains to be stopped completely
John confirmed that it takes a very long time (even years) for the Google systems to completely stop crawling a domain, even after they are redirected.
Domain Redirects Should Remain in Place Permanently
Google recommends that domain redirects should remain in place for a significant amount of time, at least a year, but it’s better to keep it in place as long as possible whilst you’re still seeing users or bots accessing the old domain.
Google Follows More than 5 Redirects In Separate Crawl Cycles
Google follows a 5 redirects during one crawl cycle, but they will continue following the redirect chains later. Once they find the final URL in the redirect chain, they will focus on that URL.
Use 301 Redirects to Inform Google of Your Preferred URL Structure
If you have a mixture of www. and non www. URLs on a site, the best way to inform Google of your preferred URL structure is to add 301 redirects with a consistent preferred domain choice.
Check Cached Page to See if Redirect Has Been Picked up by Google
Check if Google has switched the canonical version after a redirect by seeing if the cached version of the page is the target page. You can also use the GSC URL Inspection Tool to check the canonical version.
Keep Old Domain & 301 Redirects for as Long as Possible After Domain Migration
John recommends maintaining 301 redirects from an old domain to the new one for at least a year after migrating. However, users may still access the old domain years after the migration, so consider keeping the redirects for as long as possible. Also try to keep ownership of the old domain so spammers don’t misuse it.
Performing URL Rewriting is the Best Way to Change the URL Structure of a Site
If you are changing the URL structure of a website, John recommends keeping the old URLs and rewriting the URLs on the server-side, if possible. This is because, from Google’s point of view, there is very little change and it’s easier to understand the content than having to reprocess all of the new URLs. If you are not able to keep the old URLs, ensure you 301 redirect from the old ones to the new ones. A redirect is a much stronger signal that you are moving content to new URLs than canonicalising them.
Use Crawlers to Detect Internal Links to Redirecting URLs After Migration
Use crawlers like DeepCrawl to detect internal links pointing to a redirecting URL after a migration.