Not all posts returned in search

I have a multisite with 15 sub-domains. I've installed the latest "Post Indexer" and "Global Site Search". I've re-indexed my sites in "Post Indexer" and stats indicate 794 posts divided amongst the 15 domains. When I search from the site-wide search form on the main site it will only return results from 2 of the sub-domains. It seems to be ignoring the others. Many of the sub-domains have the same keywords in tittles and content so searching for various keywords should be returning results from most of the 15 sub-domains. I've gone through and checked individual site settings and all seem to be the same. Any Ideas for what I might be missing here?

Thanks,
Larry