DIR and POS

It was my understanding that WHEN you used DIR on a SPC, that
one could use POS to move "the current" byte address, like in:

DCL DD ZZZ CHAR(256);
DCL SPCPTR .ZZZ INIT ZZZ;

DCL SPC XXX BAS(.ZZZ);
   DCL DD AAA BIN(4)  DIR;
   DCL DD BBB BIN(4)  DIR;

   DCL DD CCC CHAR(100) DIR POS(9);
      DCL DD CC1 BIN(2) DIR;
      DCL DD CC2 CHAR(8) DIR;

   DCL DD DDD CHAR(50) DIR POS(9);
      DCL DD DD1 CHAR(10) DIR;
      DCL DD DD2 CHAR(10) DIR;

The idea is that there are two substructures CCC and DDD
sharing the same area (or at least the first 50 bytes).

This does not seem to work, instead one has to code:

DCL SPC XXX BAS(.ZZZ);
   DCL DD AAA BIN(4)  DIR;
   DCL DD BBB BIN(4)  DIR;

   DCL DD CCC CHAR(100) DEF(XXX) POS(9);
      DCL DD CC1 BIN(2) DIR;
      DCL DD CC2 CHAR(8) DIR;

   DCL DD DDD CHAR(50) DEF(XXX) POS(9);
      DCL DD DD1 CHAR(10) DIR;
      DCL DD DD2 CHAR(10) DIR;

Is recollection wrong or has this changed? A long time ago,
the DEFs were not needed, you could just do as the first
snippet and it would work (IIRC).