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.
Google Measures Sitemap Trust
Google has a trust rating per Sitemap, based on incorrect use of last modified data. Google can learn that the last modified date is providing useful information which increases the trust. Otherwise it will start to ignore the last modified dates.
Crawl Errors Priority Metric includes Mixture of Signals
The priority metric for crawl errors in search console is a mixture of pages being returned in search results, included in Sitemaps, and if it has internal links. The higher the priority are the ones Google thinks might have content which Google wants to index.
Add Last Modified to Redirects in Sitemaps
When Redirecting URLs include them in a Sitemap with a last modified date set after the redirect was put in place, it will encourage them to be crawled more quickly
Last Modified In Sitemaps Aids Crawling
Google thinks the Last Modified date in an XML Sitemap can be very useful to help them recrawl URLs, and they also support RSS and Atom feeds.