Your select statement,

SQL>select TO_DATE(TO_CHAR(sysdate,...

is equivalent to

select sysdate...

And whenever you select a date, SQL Plus has to convert it to a character format before it can display it on the SQL Plus output screen.

The four-digit year IS being retained internally ...until you display it on the screen. If you just set the default date format for displaying dates to include the four-digit year, you will see the full year:

SQL> select SYSDATE mydate from dual;

MYDATE
---------
14-NOV-05

SQL> alter session set nls_date_format = 'MM/DD/YYYY';

SQL> select SYSDATE mydate from dual;

MYDATE
----------
11/14/2005

SQL> select TO_DATE(TO_CHAR(sysdate, 'MM/DD/YYYY'), 'MM/DD/YYYY') mydate from dual;

MYDATE
----------
11/14/2005