Comments now showing “Comments are Closed”

It’s either I’m missing something and just don’t understand, or something has gone hinky. (I’m hoping it’s the latter, but I’ll gladly admit that it might be the former.)

On any posts that are posted prior to February 23, 2017 (inclusive), the comments are now listed as closed or the comment textbox is just not showing. Everything posted after this date is fine. I have checked two different sites and have the exact same issue on both sites.

I don’t remember making any changes or setting any option that says to disable the commenting on pages prior to the date indicated above. It might be just a coincidence that this date roughly corresponds to the release date of WordPress 4.7.3 (of which both sites are running). Then again, I look at the clock on my computer and it is possible that the window for commenting on posts is set to one month (My clock says today is March 23, 2017. Yes, I’m a day ahead of the rest of the world. That’s what happens when you live in New Zealand.)

Is there some other setting that I know nothing about?

I would like to re-enable comments on my posts that are older than a month. Please advise.

Judy L Mohr