What happens to old posts if I change something in a sidebar?

I initially worried that if I changed something in a widget assigned to a page, like the copyright date, it would wreck havoc with older pages. But a cursory investigation of my site indicates that I did that last year (updating all sidebar copyrights from 2016 to 2017) and it didn’t mess up anything posted earlier. Which then raises the question of whether I have to change this date in every different sidebar? (I’ve slept since Jan. 2017 and have no recall of what I did then!)

I found a plugin that will change the date in the footer copyright. For me, with one site, that’s actually easy enough to change. But before I go through and change all of the copyrights on 13 different sidebars, is there an easier way to do this that I’m missing?

The page I need help with: [log in to see the link]