@S.Carnahan Based on the answer linked above, it seems a reasonable guess that when completeness was blacklisted, @ToddTrimble communicated with Stack Exchange staff. So he might be in a good position to say whether this was problematic and whether they are willing/unwilling to do so.

To include some context here (so that others do not have to look for it in the transcript):

@MartinSleziak To be honest, I have no recollection that they ever replied. I have more than one avenue to try to reach them, so let's see if I can find out.

Well, the comment saying that it was blacklisted is also kind of reply.

Judging by your post you have contacted them in some way.

> Update: After removing completeness tags by hand (from the 7 posts that used it), I had put in a request to SE Community Management to blacklist that tag. I've not heard back from them though.

The only reason I've asked about this was that from S. Carnahan's message here in chat it seemed that even after reaching some consensus on meta, getting SE to blacklist a tag might still be complicated.

@MartinSleziak True, but my comment speaks more about my lack of knowledge of whether blacklisting is considered problematic or of the degree of their willingness. (I'd think they'd generally want to give knowledgeable mathematicians the benefit of the doubt; acting otherwise would seem to be really capricious.)