I've been thinking a separate key with the nevent files backed up regularly is a good way to track shitty behavior by npubs.
A list of npubs used for a mute list or label doesn't currently tell you how each npub got on the list. If you instead had a mute list of every npub tagged, reposted, or quote posted by a certain other npub, then reposting a genocidal Zionist post from an npub that only reposts genocidal Zionist posts would allow that post to go in a mute list of genocidal Zionist posters while having the specific example immediately available.
This won't be allowed to work at the network level for a while, because devs want malware that enables abuses of power and this undermines mute list manipulators or whatever. In the mean time, it's a good method at the individual level, as long as you keep backing up the posts so later you have your list ready when the network has tools available to make it more useful.