In a previous topic about the max storage period of files, we were informed that Cloudflare stores the files for one month. This may explain why the headers issued to the end users are 31d.
However, this figure is considered low and is being heavily penalised in the metrics about the quality of our sites.
I think we should be able to issue headers for about 1 year to be on the safe side.
This is irrelevant to what Cloudflare is doing. I mean Cloudflare can stop storing for economy reasons the files in a month. But the user who visits the site after two months, should be using his locally stored file (if available). If the header is set to 1month, he will have to re-issue the request!
I hope this makes sense.