Why extra blanks in stat() IFS data structure?

Why the extra blanks in the stat() data structure for the stat() IFS API's?
This does not match the defined prototypes in the Information Center, C, or
QSYSINC/SYS(STAT).  See QSYSINC/SYS(TYPES) for definitions of some
variables.
In order to get the correct values using stat() and lstat(), blanks must be
inserted in certain places.  On the other hand, stat64() and lstat64() data
structures match exactly with the Information Center, C, and
QSYSINC/SYS(STAT).  LARGE_FILE_API is automatically defined when using
these stat64() API's.
For those not familiar with any of these API's:
Use lstat() instead of stat() to get attribute information distinguishing
symbolic links from other objects.
Use lstat64() or stat64() in order to get information on files over 2GB.

Below, shows stat and stat64 data structures (same for lstat).  Why is
st_reserved1 and st_reserved2 required for RPG but never defined for the
Information Center, C, or QSYSINC/SYS(STAT)?  The stat64() data structure
doesn't need those spaces.  So, why does stat() need them?
So, the definition for these API's (the stat() prototype is an example but
would be the same for lstat(), stat64(), and lstat64()):


      * Retrieve information about an IFS file
     D stat            PR            10I 0 ExtProc('stat')
     D  path                           *   Value Options(*String)
     D  buf                            *   Value

      * stat data sructure
     D p_statDS        S               *
     D statDS          DS                  Based(p_statDS)
     D  st_mode                      10U 0
     D  st_ino                       10U 0
     D  st_nlink                      5U 0
     D  st_reserved1                  2A
     D  st_uid                       10U 0
     D  st_gid                       10U 0
     D  st_size                      10I 0
     D  st_atime                     10I 0
     D  st_mtime                     10I 0
     D  st_ctime                     10I 0
     D  st_dev                       10U 0
     D  st_blksize                   10U 0
     D  st_allocsize                 10U 0
     D  st_objtype                   11A
     D  st_reserved2                  1A
     D  st_codepage                   5U 0
     D  st_ccsid                      5U 0
     D  st_reserved3                 60A
     D  st_ino_gen_id                10I 0


      * stat data sructure for large files
     D p_statDS        S               *
     D statDS          DS                  Based(p_statDS)
     D  st_mode                      10U 0
     D  st_ino                       10U 0
     D  st_uid                       10U 0
     D  st_gid                       10U 0
     D  st_size                      20I 0
     D  st_atime                     10I 0
     D  st_mtime                     10I 0
     D  st_ctime                     10I 0
     D  st_dev                       10U 0
     D  st_blksize                   10U 0
     D  st_nlink                      5U 0
     D  st_codepage                   5U 0
     D  st_allocsize                 20U 0
     D  st_ino_gen_id                10I 0
     D  st_objtype                   11A
     D  st_reserved1                 55A
     D  st_ccsid                      5U 0

     D FilPath         S           5000A
     D statSize        S             10I 0
     D S_IFDIR         S             10U 0 Inz(20000)

     C                   Eval      statSize = %Size(statDS)
     C                   Alloc     statSize      p_statDS
     C                   Eval      FilPath = '/dir/file.txt'
      * If file
     C                   If        stat(%Trim(FilPath):p_statDS) = 0 and
     C                             st_mode > S_IFDIR
     C               whatever code you want
     C                   EndIf
     C                   Dealloc                 p_statDS


Thanks,
Craig Strong
craigs@dekko.com