I found that renaming CSS file names using the hash of the contents does not always work because any changes to dependencies (e.g. images) won't always bubble up to the CSS. I forget all of the reasons why it didn't always work, but it I think it had to do with CDN invalidation for files that I could not-rename (e.g index.html).

The process I use computes the hash of every file and creates a dependency map then I use the hash of the contents of a file and its dependencies to rename the file.