I believe that to be true. It was suggested that you should book a partner flight segment at the front end of a RTW itinerary in J with a waitlist for F, since you can't change the itinerary once the first segment commences (return flights would be 18 days out). And the connections work wonderfully if ORD-FRA via LH paired with FRA-SIN-DPS via SQ, but I very likely could end up with LH in J for an overnight segment (not my preference for O/N). The SQ segments in F would extend across daylight into nighttime with a noon arrival (local time) in DPS, so I would get to experience the full range of privileges flying SQ in F