Grunnt never let go of Miss Spook until an event the other week - he didn't let me have the event girl, but he gave up Miss Spook after about several months of trying.
Edwarda was stubborn and I had to go back to her many times after completing the world to get the remaining 2 girls.
Donatien still has 2 girls to give. It was a miracle he gave me the 1. He still refuses to let go of the others after months and now I am concerned about him having the new Legendary girl for the upcoming event.
Silvanus easily gave up the girls, but Bremen and now Finalmecia are even more stubborn than Edwarda and Donatien.
As for event drop rates... I usually cannot get a drop for 3 events, then I'll get 1-3 girls from the 4th event... then the next 3 events = nada.
The last legendary event, the devs had legendary affection gifts as an option WITH the girls - so the villain could drop the girl or a legendary gift. I'll I could get were the gifts. They would never drop the girl. I hope the devs do not do that again for this upcoming legendary event.