def _check_FITS_extvers(img, extname, extvers):
    """Returns True if all (except None) extension versions specified by the
    argument 'extvers' and that are of the type specified by the argument
    'extname' are present in the 'img' FITS file. Returns False if some of the
    extension versions for a given EXTNAME cannot be found in the FITS image.
    """
    default_extn = 1 if isinstance(extname, str) else 0

    if isinstance(extvers, list):
        extv = [default_extn if ext is None else ext for ext in extvers]
    else:
        extv = [default_extn if extvers is None else extvers]

    extv_in_fits = get_extver_list(img, extname)

    return set(extv).issubset(set(extv_in_fits))