I found an example of a Delta fare where the first letter of the Fare Code does not match the Fare/Booking class. Outbound Feb 28, ORD-UIO, returning March 5, UIO-ORD in Business. Delta's site offers a First Class ticket with outbound in I and return in Z, with 150% MQM accrual (total 8884), which is correct for I/Z. But the Fare Codes are: UNNA0NFW (outbound) and TNNA8UFW (return). Note I/Z don't appear anywhere in the fare codes, let alone in their first letters! Per Delta's logic, these fare codes would be considered U/T class fares, and earn 100% MQMs, which is not correct even as per Delta's booking site!

Is this something that is common for fares to South America? And most agents don't understand this?