Originally Posted by
bungiefanNA
It's not. The JP Trust post lists more detailed requirements than the NA one, and the patch was related and clarified what was needed, though they haven't updated the English post.
If you go get Trusts right after you watch the vocal song cutscene in CoP, both are available. If you see the next cutscene, both become locked again, and Ulmia becomes available after finishing Storms of Fate, while Prishe becomes available after finishing Apocalypse Nigh and having your mission log say The Last Verse for Zilart and Promathia progress.