INTDATE(ANSI) instructs the compiler to use the Standard COBOL 85 starting date for integer dates used with date intrinsic functions.
Day 1 is Jan 1, 1601. INTDATE(LILIAN) instructs the compiler to use the Language Environment Lilian starting date for integer dates used with date intrinsic functions. Day 1 is Oct 15, 1582.

INTDATE option syntax

            .-ANSI---.     
>>-INTDATE(-+-LILIAN-+-)---------------------------------------><

Default is: INTDATE(ANSI)

Abbreviations are: None

With INTDATE(LILIAN), the date intrinsic functions return results that are compatible with the Language Environment date callable services.

Usage note: When INTDATE(LILIAN) is in effect, CEECBLDY is not usable because you have no way to turn an ANSI integer into a meaningful date by using either intrinsic functions or callable services.
If you code a CALL literal statement with CEECBLDY as the target of the call when INTDATE(LILIAN) in effect, the compiler diagnoses this and converts the call target to CEEDAYS.

related tasks  
Using date callable services