Decode query truncates a date
As a_horse indicated, select min(date)... is sufficient.  The DECODE and multiple conversions just slow things down without accomplishing anything.  Even as parts of queries, you should eliminate this needless processing.

As Phil indicated, the displaying of dates is controlled by the NLS_DATE_FORMAT parameter and can be altered to display dates as you wish.  This does change how the queries run (unless there are missing format specifications or SQL injection is being done).  Change the display format like this:

 ALTER SESSION SET NLS_DATE_FORMAT='YYYYMMDD';


When doing a to_date on a two digit year, use YY when you want the first two digits of the year to match the current year, but use RR when you want the first two digits to be 20 for years ending in 0-49 and 19 for years ending in 50-99.  See the SQL Language Reference for more information:


  The RR datetime format element is similar to the YY datetime format
  element, but it provides additional flexibility for storing date
  values in other centuries. The RR datetime format element lets you
  store 20th century dates in the 21st century by specifying only the
  last two digits of the year.
  
  If you use the TO_DATE function with the YY datetime format element,
  then the year returned always has the same first 2 digits as the
  current year. If you use the RR datetime format element instead, then
  the century of the return value varies according to the specified
  two-digit year and the last two digits of the current year.
  
  That is:
  
  
  If the specified two-digit year is 00 to 49, then
  
  
  If the last two digits of the current year are 00 to 49, then the returned year has the same first two digits as the current year.
  If the last two digits of the current year are 50 to 99, then the first 2 digits of the returned year are 1 greater than the first 2
  digits of the current year.
  
  If the specified two-digit year is 50 to 99, then
  
  
  If the last two digits of the current year are 00 to 49, then the first 2 digits of the returned year are 1 less than the first 2
  digits of the current year.
  If the last two digits of the current year are 50 to 99, then the returned year has the same first two digits as the current year.
  
  
  
  The following examples demonstrate the behavior of the RR datetime
  format element. 

SELECT TO_CHAR(TO_DATE('27-OCT-98', 'DD-MON-RR'), 'YYYY') "Year" FROM DUAL; 
Year
---- 
1998 

SELECT TO_CHAR(TO_DATE('27-OCT-17', 'DD-MON-RR'), 'YYYY') "Year" FROM DUAL; 
Year
----
2017