Hi guys.. i have been submiting my sitemap regularly,and everything was working just fine until 2 weeks ago. I used to have a total 8600 URL and around 3200 Indexed URL... but suddenly the number of indexed URL started decreasing... ????? first 1,200 ... 600 .. and now 324! and i my total of sent via sitemap URLs is around 9 thousand now.. What is going on ??? any ideas ?
You can't trust those numbers if you are deleting/submitting sitemaps instead of updating the existing sitemap. I believe the number shown is actually the number of URLs in XML sitemap verified to be indexed. One reason is that "indexed" gets reset everytime you delete/add an XML sitemap, yet all "prior indexed" pages remain strong in SERPs. That is one of the reasons I believe Google Webmaster Tools "indexed" number is... Well, incorrect. I also ran another experiment (see link) which proves that.