Field note 14 is a 100% drop rate from the Sartauvoir duel so if you've really done these skirmishes / critical engagements this much then you should of had quite a few chances at doing the duel yourself. Just RDM cheese it and the boss dies before doing more then 3 mechanics which are simple aoe dodges. The drop rate is low on purpose from those fates to keep the reward from the duel desirable so your choice not to pick the easiest way of getting it.