When I type: site:www.mysite.com in Google, sometimes I get 7 search results pages and sometimes 15 (and sometimes another number). Why is Google showing different numbers of my pages indexed at different times? Has anyone else experienced this?
The reason you get different figures at different times is because the datacenter that your "www.google.com" points to changes and not all the datacenter is updated with the same figures. In fact, on average your "www.google.com" will change its datacenter every 1-2 minutes so getting the same result isn't always a guarantee.
Google may anytime remove any page from their index or add any page in their index. So site: operator will not always give you same result.
there are like millions or maybe billions of site/pages to crawl and index everyday and only one google.. that's the reason why they have to update the indexed pages of every site.. regular gathering of links and proper site linking can help to maintain site indexed..
Everyone has experienced this type of thing. Reason: Google is not the perfect machine that you think it is. Bompa