Why do we need to re-render all sequences after an update?

[Brit.b]

I am wondering why we need to re-render all sequences after an update? I never had to re-render any sequences after updates before 2 years ago - the render/preview files always transferred over onto sequences in the new updates. (I've been using this software for over 20 years.) This current update is the third one in a  year, and I am spending many days and nights re-rendering all my many dozens of recent sequences. Some sequences are taking several hours to re-render. I posted this Is there any way to retain rendering files from the previous version? during the last update. But none of the proposed solutions worked. Nor can I get through to Adobe support. (I gave up that sisyphean task ages ago.) Any suggestions? Thanks in advance.

[Brit.b · Accepted solution]

OK, an update. I updated my Nvidia video card driver, opened another project (on which I had not yet  re-rendered the sequences) and most (though not all) render/preview files came up green...they worked.