COBOL didn't have a date field, except for a few Microsoft builds. Most still had a 6 digit numeric field which was left up to the programmer to decide how to use it.
Because of the year 2000, and difficulties to convert database files, local conventions started using a cut-off date to decide if a date would be in 1900 or in 2000. And that depended upon the use cases, e.g. there would be a difference between birthdates and order dates.
So, the only reason why a program would use this, would be a local program convention for some reason, but not a general one for Cobol.