I was going to post much the same thing so I'll sort of bump this thread.
I followed the Scrubber IVs (there were two walking the same route, which I believe to also be improper though less relevant clearly) along a dozen loops and they aren't despawning when they get all the way back into the castle so they can never even theoretically respawn as Duster V without a zone reset (or jacking up the PH but they're zone faction and clearly not intended to be killed).
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