Here is the D fare
Fare Code - DFFUS
CHANGES/REFUNDS SEE TEXT RULE

And here is the one for the Z fare:
Fare Code - ZLP8US

CHANGES/REFUNDS ORIG AREA 1
CANCEL-NON REF BEFORE/AFTER DEPART
CHANGE-100.00 USD
ORIG INDIA
FURTHER RESTR APPLY SEE TEXT RULE
FOR ALL CONDITIONS SEE TEXT RULE

I clicked on view full fare rules and it didn't give me anything on the D fare. It said the following on the Z fare:
CHANGES


AFTER DEPARTURE
CHARGE USD 100.00.

TICKETS MUST BE REISSUED WHEN ANY VOLUNTARY
CHANGE IS MADE. CHANGE FEE PLUS ANY DIFFERENCE IN
FARE MUST BE COLLECTED AT TIME OF CHANGE OR
CHANGE WILL NOT BE PERMITTED.
.---
NEW FARE WILL BE RECALCULATED USING FARES IN
EFFECT ON THE PREVIOUS TICKET ISSUE DATE AND
UNDER THE FOLLOWING CONDITIONS-
-IF SAME BOOKING CLASS/SAME RULE- NEW FARE MAY BE
LOWER / EQUAL / HIGHER THAN PREVIOUS FARE AND-
A. MUST COMPLY WITH ALL PROVISIONS OF
ORIGINALLY TICKETED FARE
B. OR MUST COMPLY WITH ALL PROVISIONS OF THE
NEW FARE BEING APPLIED.
- IF DIFFERENT BOOKING CLASS- NEW FARE MAY BE
EQUAL / HIGHER THAN PREVIOUS FARE AND-
A. MUST COMPLY WITH ALL PROVISIONS OF ORIGINALLY
TICKETED FARE
B. OR MUST COMPLY WITH ALL PROVISIONS OF THE
NEW FARE BEING APPLIED.

So I assume that on Z fare, it will be $100 plus fare difference. But what is it for D fare. Is it just DL.dumb acting up and not telling me what the full fare rule is?