I've never renamed the files and my saves have always been there after an update. File name doesn't matter for this.
you're using chrome-based browser.
It does for me somehow. Someone earlier mentioend Firefox being different with how it works with the saves?
I'm not smart enough to know.
in chrome, any html opened from any folder on your pc will have access to the data stored by any other html on your pc. one html app can read, leak, alter, and delete stored data from every other html app. not great for security.
firefox requires that storage access is tied to the exact same folder and name of the html file to prevent that. though it can be changed if you don't care about security risks
exactly, you have to be really brave (or stupid, or both) to trust such security policy.
nevertheless, same behavior can be achieved in firefox by setting `security.fileuri.strict_origin_policy` to false in `about:config`.