The GET orderables/id should support If-Modified-Since HTTP header for all of the incoming requests. If the header is present, the request should only return a whole representation if the server modification date of the given orderable resource is later than the date provided in the If-Modified-Since request header https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Modified-Since
if the dates are the same or the version in request header is latter than the server version, the request will return response code 304 Not Modified and the response body will be empty. The Response header Last-Modified should contain the same value that the modified date field.
If-Modified-Since request header is supported in orderables/id endpoint but is optional
If the header is not provided, the endpoint returns the response as it used to
If the header is provided, the request returns a 200 response with the body only if the server version is latter by comparing the modification dates in the header and the modified date in server resource
If the header is provided, but the header version is the same or latter than the server version, the endpoint returns 304 Not Modified and doesn't attach the request body
Last-Modified header should always be present