We recently added a sitemap to our site but didn't exclude unpublished items (which, unless you're logged in as an admin, will 404). Google started trying to crawl them and as a result, we saw a huge increase in the number of 404s in the Google Webmaster tools.
We've since corrected the sitemap and now those items are not included, however the graph still indicates there are a high number of 404s. We can mark these URLs as "fixed" in the webmaster tools, but they aren't fixed - they're still 404ing, they just shouldn't be crawled and indexed.
Is it possible to tell Google not to crawl these? Will I need to add these 40,000 links to our robots file? And will these 404s be causing an issue for SEO?