In that situation the metadata is no longer part of the 'file' then, and would be lost by a 3rd party copy function unless extra API functions are used to copy

In that situation the metadata is no longer part of the 'file' then, and would be lost by a 3rd party copy function unless extra API functions are used to copy the metadata. At this point, it might as well be a "resource fork" or whatever you want to call your secondary file contents at the fs layer shrug