I had inadvertently enabled the setting to disable comments on any post older than 14 days. This has been fixed. I do want people to be able to get in touch with me about articles I’ve written, and with my posting frequency, it would be better to always allow comments and deal with the occasional spam-bot. So, comments are on. I’m going to poke around a little, and if I find posts with comments turned off, I’ll just get out the SQL editor and go to town.