That requires preprocessing on the client and there are some ppl who has.. weird assumptions about how the dates should be written.

The version file can be quired at least the two ways:

the ETag/If-Modified-Since way (metadata only)

content itself

The best part with the last one - you don't need semver shenanigans. Just compare it with the latest dloaded copy, if version != dloaded => do_the_thing