How to deal with cross-site exact duplicates?

Question

These questions:

https://superuser.com/q/595977/173718

https://stackoverflow.com/q/16571901/1014938

Are exact duplicates, so I attempted to flag one as such, and got an error message along the lines of "exact duplicates must be on the same site". When I then tried to flag it as "other" with the text "exact duplicate of (link)", I got another error message saying that I should flag it as an exact duplicate with the relevant ID.

This is more than a little confusing. I've just read one or two questions here on Meta which suggest that cross-site dupes are not, in fact, discouraged (which seems crazy to me, but there you go). If that is the case, it might be worth saying so more clearly when someone attempts to flag them (or at least having a canonical FAQ here that people can be pointed to).

Answer 1

From flagger perspective, cross-posts are rather comfortable "target", mainly because there is a solid reference that justifies flagging - 'cross-posting' tag wiki at MSO:

Cross Posting refers to posting the same question over multiple Stack Exchange sites. Cross-posting is strictly frowned upon as it leads to fragmented answers splattered all over the network. If you spot a user cross-posting, please make use of Moderator Flags to inform the Moderators...

Based on my reading of above guidance, I have successfully flagged cross-posts using custom ("Other") flag with message that explicitly refers to tag wiki:

cross-posted at <other site name>: <question URL at other site> (flagging per https://meta.stackoverflow.com/tags/cross-posting/info)

• ^{So far, I have flagged several dozens posts at Programmers, with only a single decline. Decline reason for that single failed flag could likely be successfully challenged, but I just didn't bother to compose sufficiently researched and polite appeal at meta.}

---

Couple additional considerations for flaggers willing to minimize risk of declines.

• Leave decision on what to do (close, delete, keep...) at discretion of moderator. Note that tag wiki don't specify concrete action => anything you'd "push" for would be on your own risk. Note also that "strictly frowned upon" statement may have exceptions: for an example when cross-posting was considered appropriate, refer to this discussion at WP meta:

  Cross posting is generally a bad idea and I wouldn't suggest it for questions that aren't truly suitable for both sites, but this one is...

• Stick with flagging at one of involved sites (although technically, cross-posts allow one to flag at both). Assuming that for cross-site issues moderators of involved sites may communicate, flagging at both sites carries a risk of being considered redundant.

• Avoid flagging in series. Moderators may prefer to deal with single list of problematic posts instead of handling a bunch of similar flags submitted in quick succession. If you happen to discover several cross-posts, safer way would be to describe this issue in site meta or in chat, then flag one of them with message like:

  I believe there is an issue (cross-posting) with this and couple other posts, please take a look here: <refer to chat or meta>

Answer 2

There's no such thing as a cross-site duplicate.

Each site has its own user community and scope. It's challenging enough for a community to run itself without having to worry about what's going on on some other site. That's part of the reason that migrations are so difficult; they require accurately knowing the scope of both sites to get it right.

You cannot choose an alternate site for closing as a duplicate, because duplication is (and always has been) considered a single-site phenomenon for purposes of closing.

Cross-posting is discouraged, however. If you see it, and you don't see any value in the question being on two sites, flag the question on the site where it is less on-topic, using the custom description, and explain that it is a cross-post, and should be removed.

The way you identify cross-posts is that they are usually copy/pastes; there's no effort on the part of the OP to tailor the question for each site's scope. Posting a question on two different sites is perfectly fine, if the OP can make the question relevant for each site.

Answer 3

If the question is generally the same but is asked in good faith by different users, and is on topic on both sites, then it is fine that it exists on both sites. If you think a question on one site would be beneficial for readers on the other site, leave a link in the comment section.

(That George Stocker will want to delete later.)

If the question is cross-posted by the same user, then flag it, as user cross-posting is discouraged.