I do wonder if locking a topic is the right option. Not tried, but once locked can one delete what you have written? One would assume locked to stop some one putting in inappropriate content, however as the author if you realise you have made an error one should be allowed to correct it. So to ensure inappropriate content can be removed, should the tread not be deleted rather than locked?
I know I started on this forum before 2008, and I googled a topic once only to find a pre-2008 comment I had made, which although correct at time of posting, is no longer correct, be it 2, 5, or 10 years, it does need a cut off point where old posts are deleted.