i think setting older post for comment review is the best approach closing it, especially for casual reader makes them unable to comment when they found it. some old post have value some times after the post is done especially for pre trends idea. some blog and web site i have seen in 2001-2004 about the mortgage questionable behavior are probably the place where reference and comments should have been place last year with reason. blocking it completely is not good. review is sometimes the only options, many use old post to get unotice and make very big mess.