This was brought up again recently by Smmenen, and following staff discussion, we agree that, given current posting volumes, the rule is no longer required, so I have removed reference to it from the rules.
I note that the examples in the rules are not exhaustive, and necros would still need to not breach any other rules, e.g. threads still need to be relevant (threads from 2004 would have a high bar to meet, for example), but we will take a common sense approach, and assume users will do the same.
(It seemed appropriate to necro an old thread about necros to announce this policy change, somehow...

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