Google’s John Mueller recently answered a question about how Google responds to staggered site moves where a site is partially moved from one domain to another. He said a standard site move is generally fine, but clarified his position when it came to partial site moves.
Straight Ahead Site Move?
Someone asked about doing a site move, initially giving the impression that they were moving the entire site. The question was in the context of using Google Search Console’s change of address feature.
They asked:
“Do you have any thoughts on this GSC Change of Address question?
Can we submit the new domain if a few old URLs still get traffic and aren’t redirected yet, or should we wait until all redirects are live?”
Mueller initially answered that it should be fine:
“It’s generally fine (for example, some site moves keep the robots.txt on the old domain with “allow: /” so that all URLs can be followed). The tool does check for the homepage redirect though.”
Mueller’s initial response was based on the assumption that the site move is happening normally, where the entire site moves at once. What he does not know is that the person asking the question is holding back key information.
He is assuming that he is commenting on a standard site migration where a small number of residual URLs are lagging behind. In that context, Google’s systems can still interpret the move correctly because the primary signal, the homepage redirect, establishes a clear destination for the site as a whole. The remaining URLs are treated as stragglers rather than evidence of an incomplete migration.
His answer also shows how the change of address tool is designed to work. As long as Google can see a clear redirect from the old homepage to the new one, it can assume that the entire site has moved or is in the process of moving, even if some URLs are still serving traffic temporarily. The person asking the question afterward returned to the discussion to let Mueller know that parts of the site are intentionally staying behind, which turns what looked like a temporary lag in a site migration, itself not unusual, into something more problematic than was initially apparent.
Google Explains Why Partial Site Moves Are Problematic
His opinion changed however after the OP responded with additional information indicating that the home page has been moved while many of the product and category pages on the old domain will stay put for now, meaning that they want to move parts of the site now and other parts later, retaining one foot in on a new domain and the other firmly planted on the old one.
That’s a different scenario entirely. Unsurprisingly, Mueller changed his opinion.
He responded:
“Practically speaking, it’s not going to be seen as a full site move. You can still use the change of address tool, but it will be a messy situation until you’ve really moved it all over. If you need to do this (sometimes it’s not easy, I get it :)), just know that it won’t be a clean slate.
…You’ll have a hard time tracking things & Google will have a hard time understanding your sites. My recommendation would be to clean it up properly as soon as you can. Even properly planned & executed site migrations can be hard, and this makes it much more challenging.”
The point Mueller is making is that Google does not treat a migration as a gradual or modular process. Its systems expect a site move to present a clear before-and-after state, not a slow and gradual process. When only the homepage moves and large portions of the site remain behind, Google cannot reliably determine which domain represents the site’s primary identity. As a result, signals are not cleanly reassigned, reporting becomes unreliable, and both domains must be evaluated in parallel rather than as a single continuing site. This is why Mueller characterized the situation as messy rather than transitional. It is not a temporary inconvenience, but a state where Google’s systems are forced to operate with incomplete and conflicting inputs until the site migration is finished.
Related: Google: Don’t Combine Site Moves With Other Big Changes
Google’s Site Understanding
Something that I find intriguing is Mueller’s occasional reference to Google’s understanding of a website. He’s mentioned this factor in other contexts in the past and it seems to be a catchall for things that are related to quality but also to something else that he’s referred to in the past as a relevance topic related to understanding where a site fits in the Internet.
In this context, Mueller appears to be using the phrase to mean understanding the site relative to the domain name.
See also: It Takes Months For Google To Evaluate Website Quality Across The Web
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