I'm currently managing Webmaster Tools for some Wordpress sites and I'm curious as to why none of the sites are showing more than 1000 pages submitted. Some of the sites are much larger but I can't find any documentation that would limit the number of submitted pages.
Is it possible to inform us about following?
1) Which sitemap generator is used?
2) What is/are the sitemap(s) showing itself? (meaning > or < then 1000 url's)
3) How long (month/year) do those websites exist.
4) How long (month/year) is google crawling these sites.
FYI:(from google, https://support.google.com/webmasters/answer/183668?hl=en)
A Sitemap file can contain no more than 50,000 URLs and must be no larger than 50MB when uncompressed. If your Sitemap is larger than this, break it into several smaller Sitemaps
Imho no limits from google side. (FYI, the only max is 50k url's/50MB in 1 sitemap but you are alowed to have a max of 50k sitemaps means...2.5 billion URLs)
-Also another reference was found here on Pro Webmasters: Google Sitemap Limits?