You could try dashboard>>presentation>>sidebar widgets>> then locate the archives widget open it and click save. Hopefully, this will re-configure the archives widget and the “0” will disappear but I’m not offering a guarantee.
Thank you for feedback! I did find a funky post (the one I had tried to postdate) with the year 1970 on it. I deleted it. Then I tried redoing the widgets (removing archives, saving putting it back in). The 0 is still there.
It’s not a huge deal, as we’ll be porting over onto a server in the fall, I think, so this will all be redone. I’ll keep playing with it in the meantime.