If I modify a CSS file or a JS file, as far as I know, I/our customers have to force a full refresh to download the updated version. One could add the timestamp to the file name, but that can be cumbersome.
1. Fix this using headers that check the last modified date of the CSS/JS-file.
2. Add timestamp (last modified) in the url that's generated to download the file.
151020200651 is the date, hours and minute the last modified resource was modified.