You can read various interesting texts and tutorials
 about the Year 2000 problem, software only using
 two-digit variables for their year counter, etc.

 But did you ever take a look at a real COBOL source
 code that deals with date checking ?

 Here's one - and it's Y2K (2000/2100) proof.
 Hopefully ;)

 datpruef.cbl:  - the original german version
 datcheck.cbl:  - the english translation

 --
 ARK, 02/Jan/99

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                  347     530  65.5% -lh5- 4dc0 Jan  2  1999 cobol2000/cobol2000.readme
[generic]                  612    2271  26.9% -lh5- fb40 Jan  2  1999 cobol2000/datcheck.cbl
[generic]                  623    2259  27.6% -lh5- 7f40 Jan  2  1999 cobol2000/datpruef.cbl
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total         3 files    1582    5060  31.3%            Jan  2  1999