Google Automatically Chooses a Preferred Domain Based on Multiple Signals
Google uses many factors to determine the canonical domain including redirects, canonicals, internal links, sitemaps and backlinks, so choosing a preferred domain in Search Console is not critical.
Hreflang Data in Sitemaps May be Shown as ‘No Return’ Error Until the URLs are Recrawled
Until pages have been recrawled, you might see hreflang ‘no return hreflang’ errors in search console for hreflang data added to a Sitemap.
Sitemaps Require Absolute URLs and Recommends for Internal Links
Relative URLs are fine for internal linking, but Google requires absolute URLs for Sitemaps. Google now recommends using absolute URLs for internal linking to avoid any uncertainty about the preferred protocol.
RSS with Pubsubhubbub to get URLs Indexed
You can use an RSS feed with Pubsubhubbub to ping Google with new URLs as an alternative to Sitemaps.
Use Sitemap Index Count to Measure Indexing
Site: is not an accurate measure of indexed pages, and could be off by ‘orders of magnitude’. The Sitemap Index count in Search Console is accurate for the specific URLs submitted.
Submit Old URLs in Sitemaps when Moving Domains
When moving domains, you can submit old redirecting URLs in a Sitemap with a changed date, on either domain, to help get them re-crawled more quickly.
Sitemaps on Separate Domains Require Both Sites to be Verified in Search Console
You can submit Sitemaps with URLs on a different domain if both of the site are verified in the Search Console account.
Sitemaps Hosted in Subdirectories are Only Valid for URLs in the Same Directory
Sitemaps located in a subdirectory only be valid for URLs in that sub-directory.
Search Console Indexed URLs Counts Report Exact URLs in Sitemaps
Search Console indexed pages in Sitemaps uses exact URLs, so variations including www/non-www, trailing slash variations, etc, won’t be reported as indexed.