Importer fails to import every post

Open the WXR in a text editor and see if it contains posts from later years. If not, you will need to revisit your export settings from WP.com to make sure you’re pulling all posts.

If it does contain posts from these years, there might be a non UTF8 character breaking the import. You should be able to spot any offending characters in a typical IDE that parses XML. If this is the case, you should edit those characters and retry the import.