i recently changed theme of one of my website well 3 months ago now,so i updated webmaster tools and removed all 404 pages from the search engine using the tool on there, they removed all the pages i asked them to remove, then in december they all came back, so i removed them all again with the same tool but now they will not go , anyone any ideas why this happens, i mean to remove them and then 2 months later they all return a little strange i think
Do not redirect 301 "page not found" because search engines will re-visit and re-index the pages again. Just leave the pages "page not found" and after a few time revisiting those pages, search engines bot will stop visiting and remove those pages from its database.