Old sitemap causing 404 errors. How to get rid of it?

More than six months ago I submitted a few sitemaps to GWT for one of my sites. Later I noticed that many of the URLs in the sitemaps were wrongly formed due to a config error in the sitemap generator. I was getting lots of 404 so I removed the old sitemaps and replaced them with new ones.

Until today google is still trying to crawl a lot of those wrong URLs from the removed old sitemaps. Since the site is really big I'm getting thousands of 404 errors in GWT and I'm afraid that it may impact the crawl health of the site.

Anyone knows how to stop Google from requesting the old URLs?

You can remove those URLs from GWMT manually by page level or directory level. Click the tabs Google Index --> Remove URLs

Those pages are not actually indexed since they have never existed so it's not possible to request them to be removed.

The problem here is that Google keeps requesting those old unexistent URLs because they were listed in my old sitemap.

The only solution I managed to find is to look for a pattern in how the wrong old URLs were formed and redirect them to the correct ones using regex to match the pattern.

I'm sure that was a PITA. Sorry you had to go through that.