Confusion with autoextend on datafiles

I always thought datafiles can grow to a max of 32 GB (one block less than 32GB to be precise). But for the following tablespace I am wondering how couple of files grew beyond that (more confusing is - one of them is with autoextend ON and another OFF). Any clarification or reference document in this regard will be greatly helpful.

SQL> select file_id, file_name, bytes/1024/1024/1024 SIZE_GB, autoextensible from dba_data_files where tablespace_name='FIHROBIIX01';

   FILE_ID FILE_NAME                                                                 SIZE_GB AUT

---------- ---------------------------------------------------------------------- ---------- ---

        13 /hradmuwlk1/oracle/dbdata/app02/ofihrix01.dbf                          63.9990234 YES

        14 /hradmuwlk1/oracle/dbdata/app02/ofihrix02.dbf                                  31 NO