So last night, I was playing with my friend and I noticed that this relic might be bugged and/or lacks the proper description.
I know about how only 1 person can see the armor plates bug. But also, there's no armor plates drops. To me, armor means the vests, hence the description making sense. But the only plates you can get are from max armor drops.
Even if it's the wording that is off, during relic trials while the relic is turned off, you still cannot buy armor plates and no zombies drop them. Which is why I think it's relic affect is bugged, more then lacking a proper description.
TLDR. Bugged armor bar, no armor plate drops, cannot buy or have zombies drop plates inside relic trials with the relic on