Per my original post from three weeks ago, I'm using a coarse method to identify (and try to draw the admins' attention to) a particular pool of accounts that were created in a specific week on a handful of instances. Actively spamming bot accounts, and bot accounts on other instances, won't be caught with my method. I'm not being thorough, just looking for low-hanging fruit.
It is possible that some legitimate users' lurking accounts got swept up and deleted, but I think that's very unlikely. If an instance suddenly goes from 3 users to 60,000 users in a week, then the growth abruptly stops and none of those new users show activity, that's suspicious. If there are real people in that wave of accounts then at least a few of them should be posting or commenting, and more people should continue opening accounts over time.