Fwiw I used to work at Google and raised this internally. It is definitely something the search quality team was aware of and it affects other projects as well. Try searching for docs on Java APIs for example.
They seemed really interested in improving it and there have been some improvements but it's obviously still not there. It's a harder problem than you might expect because there are lots of links to old versions and they have lots of data that users are happy with the results from 9.6 or 10 (and indeed even after 11 is released most users are probably still looking for 9.6 or 10 docs...)
A few things we could do is add a prominent coloured banner across the top of every page saying "you're looking at docs for an old version, click here for the docs for the current version".
We could actually make the current version "canonical" but then it would be actually awkward if anyone wanted to search for older docs. And it's not true in general that every page is present in every version. We sometimes add or remove pages from the docs... That still might be the only really useful option today.
