I have a sitemap-index.xml with 7 files. After updating one of the 7 with new content should I ping Google with the index file or with the updated file?
In my index I also use lastmod so Google can see when downloading it which item is newest.
The Google help page on submitting sitemaps says:
Assuming that you're indeed providing correct
If you really want to be sure, I guess you could do it and later look in your access logs to see which sitemaps were actually fetched. If you do that, please report the results here so that we can have a definitive answer. :-)