The only special thing about the Zip file format that springs to mind as causing ambiguity is the handling of the OS-specific extra field for a Zip archive entr

The only special thing about the Zip file format that springs to mind as causing ambiguity is the handling of the OS-specific extra field for a Zip archive entry. You don't have to include an OS-specific extra field unless you want the information in that specific extra field to be available by the party trying to extract the contents of the zipfile.