struct_conn has ptnrn_label_comp_id, ...label_asym_id and ...label_seq_id as mandatory. It would seem sufficient for these data items to be implicit, since ...label_atom_id is also mandatory. It is more likely the various ...auth_... tokens would be given to improve readability of a connectivity section than the ...label_ tokens, once the essential atom_id had been given. Note similar problems exist in other categories, which could be resolved by making both the ...label_... and ...auth_... tokens implicit, rather than having one be mandatory and the other not.