I used to have 60,000 pages cached for a dynamic website. I changed this to something a lot more static and many times less pages. Today, after about a year, I got around to 301 redirecting all of those old non-existent pages to my main site. I check them just now and Google no longer has those pages. I didn't realize Google could move that fast and remove those pages so quickly. This message was just meant as an FYI.