The drop of Harbinger Eye should be increased to a 100% drop chance once you get past the corruption needed to finish the Forgotten Knights quest chain/rep (300+). I think this should be the only drop chance adjustment for Harbingers as the other items (needle) are more QOL than anything.
The reason I suggest this is because once you finish the quest chain, you are likely level 94+ and are ready to learn and progress on the Aberroth fight. Grinding out 800+ stability on a timeline, only to have the Harbinger not drop an eye is quite demoralizing, knowing you have to start over from scratch and do it all over again with another chance that an eye may not drop.