Knowing you use modules a lot helps me understand your point better. You having read and prepped for the adventure do know very well which npc is important or not.
Since I am not running modules (AND I'm well aware my players will talk to all five ships...) I approach it differently.
As far...
No, they choose one of the 5 available paths, all were ready for play. If they had chosen a 6th option, as I do not constrain their actions, then I would have had to improvise.
No. You misunderstand me.
If the players go there, and learn of the armor, of course I tell them abut it.
I'm asking if the character should know about the armor before encountering it in game.
Your post is well written and feel I understand your point.
My only question is how do you know which NPCs don't matter?
I can give a concrete example from our point of view.
Characters needed to get to some desert ruins (long journey).
Most of the trip would be by river.
There were five...
Kobolds are like elves...they adapt (mutate) to their environment/creature leader.
So traditional kobolds are doglike, the dragon worshipping ones are semi reptilian after a few generations.
And the aquatic ones are like World of Warlock murlocs....mrglwglwlg!