I think you missed the message saying "Old post: We generally do not moderate posts this old for on-topicness, substantiveness, multi-posting, and other "cleanliness" issues." when reporting old posts.
I didn't miss that message, but IIRC a moderator says its okay to report old SEO spam. And almost all thread i reported shows that same message, where some of them marked as good anyway. Maybe there's something i missed or forget here.
Edit: Now all of my reports marked as good. But some of the thread are locked rather than deleted, which means the user still enjoy benefit of SEO spamming.