It is not possible to specify which countries and regions content should rank in
There is no way to prevent Google indexing content in specific countries and regions, even if it’s not targeted to that audience. The example given was a user who wanted English pages to rank only in the US and the UK. If Google deems the content as relevant to users in other locations, there’s every chance it will be indexed there too (and nothing that webmasters can do to prevent this).
Hreflang x-default tags are required to show Google that a default URL is part of your page set
The “x-default” tag allows Google to understand that the default version is a part of your set of pages. Failure to include this could see the default version unintentionally appearing in a region’s index.
Try to Have the Fewest Internationalised Versions of a Site
Adding many internationalised versions of a website increases the complexity, so you’re better to have fewer versions if possible, especially if you have pages where you can rely on geo-targeting without hreflang. You can use Search Console and web analytics to see if people are landing on the wrong pages, and implement hreflang for those. For different language versions, hreflang can help Google to show the right version, but searches for long tail content are easily recognisable for which language version to show, so hreflang may not be necessary.
Individual Hreflang Links to Non-working Pages Won’t Affect Other Links
Google will ignore hreflang links to redirecting, non-indexable and non-reciprocating pages, but this won’t affect other hreflang links.
Use Hreflang on More Generic Pages to Deduplicate SERPs
For a more generic query like a brand name, it can be hard for Google to understand which language version a user is looking for. Hreflang tags can help here to swap out incorrect language versions by using the user’s language settings.
Having Hreflang in Sitemaps vs on Page Makes No Difference to Google
It makes no difference to Google if you choose to include your hreflang configuration in an XML sitemap or on the page itself in the head tag.
Hreflang May Not be Necessary For Translated Versions of Pages
Pages with different language content don’t necessarily need hreflang because the text is different so Google would treat them as unique pages and not as duplicates.
Hreflang is Not Required For Untranslated Pages
As hreflang is handled on a per page basis, if you have different language versions of your site but not every page is translated, it isn’t a requirement to have hreflang set up for these pages. John recommends choosing the method that best suits individual websites, this could be either including the URL in the hreflang set or not including the URL.
Hreflang Can be Implemented on Small Groups of Pages
Hreflang doesn’t have to be implemented across an entire site. Sometimes it makes sense to implement hreflang on individual pages or sections where there are problems, or where it is especially important that the correct page is shown.