The only example I could think of someone being exposed more than once was Merry (based on: once in Bree, once at Weathertop and lastly vs. the Witch-King-- correct me if I’m wrong). I imagine Frodo probably was also “exposed” more than once though I’ll be honest, I didn’t go back to check and I also wonder if his experience would be amplified or affected in some way by his possession of the Ring.
While doing that digging, I came across this quote that the Nazguls’
from The Hunt for the Ring: Other Versions of the Story, Unfinished Tales“chief weapon was terror. This was actually greater when they were unclad and invisible; and it was greater also when they were gathered together.”
Which led to more questions and made me wonder... why? Do they need to expend some energy to maintain their disguise as Black Riders which reduces their ability to instill terror? Do their rings of power help them to do so?
And finally, that led me to a hypothetical: what would happen if a Nazgul lost (or otherwise removed) one of their Rings?
These aren’t really very streamlined or yes-or-no questions and may only lead to conjecture, but I am curious what people think.