This allows Why post_number? - #3 by Kevin_Wildenradt to continue to work efficiently even if Why post_number? - #2 by sam is deleted.
And Why post_number? - #3 by Kevin_Wildenradt is arguably much prettier than Why post_number? - #9 by sam or https://meta.discourse.org/t/why-post-number/373873 which does not hint properly on the topic.