Updated css stuck on an old ver parameter

My website is hosted on GoDaddy using the WP 2011 template. Periodically, WP 2011 gets updated – which naturally means that any changes I’ve made to style.css will be overwritten. No problem: I go in to style.css and add a few commented lines to the code, the file is successfully updated, I refresh the browser and everything is fine. But when I looked at my site after the most recent WP update (4/2) and after my usual modifications to the css (4/3) it looks like the original css is still being used and not mine. I confirmed that my modified css is the one on the server. When I look at any page using Developer Tools in a browser, I see https://…/themes/twentyeleven/style.css?ver=20240402. When I change the date to 20240403, it looks fine. The problem is the ver parameter seems to be stuck on the date of the update (4/2), even though my commented .css (4/3) is on their server. Can anybody help me? Many thanks!