Generated Sitemaps Not Found

Here is my list of Generated Sitemaps:

1 sitemapindex Sep 05, 2016 04:57:23 PM
2 site Sep 05, 2016 07:10:19 PM
3 post Sep 05, 2016 06:34:44 PM
4 post_sermons Sep 05, 2016 05:31:24 PM
5 post_google_news Sep 05, 2016 05:01:20 PM
6 post_event Sep 05, 2016 03:04:36 PM
7 page Sep 05, 2016 03:04:29 PM
8 post_staff Sep 05, 2016 03:01:50 PM
9 post_epl_event Sep 04, 2016 01:02:23 PM
10 post_epl_org Sep 01, 2016 01:01:05 PM
11 post_rvs_video Aug 13, 2016 12:01:08 PM

The last 3 throw a Sitemap Log error of “Requested sitemap (xxx.xml) was not found or not enabled.” Insert “xxx” with the name of the relevant sitemap.

Why do I have these 3 sitemaps listed which are not found or enabled?

When I view my sitemapindex.xml file, I see:

Location Last Modified
http://www.mydomain.com/site.xml 2016-09-06 01:10
http://www.mydomain.com/post.xml 2016-09-06 00:34
http://www.mydomain.com/post_gallery.xml
http://www.mydomain.com/post_staff.xml 2016-09-05 21:01
http://www.mydomain.com/post_sermons.xml 2016-09-05 23:31
http://www.mydomain.com/post_event.xml 2016-09-05 21:04
http://www.mydomain.com/post_google_news.xml 2016-09-05 23:01
http://www.mydomain.com/page.xml 2016-09-05 21:04

Note that post_gallery doesn’t have a time and is, in fact, empty…and the others listed in the blockquote above are NOT in the actual sitemapindex.

Can I delete these unused sitemaps?