Can we dupe-close Story IDs when confirmation is given by what looks like the OP’s second account?

Question

You may have seen this: a new user asks a story-identification question, then a second (also new) account gives the answer (or confirms an existing answer, though usually this deleted and transferred to a comment). There is reason to believe that these two accounts are the same person for one or more of the following reasons:

• The second account acts like they asked the question, such as by saying “Thanks for helping me find the answer to my question”.
  • There are varying degrees of this. Sometimes the user even explicitly admits they lost the first account
• They have similar/identical usernames
• They have the same profile picture
  • When this is an automatically generated Gravatar, this means the same email was used for both accounts, though a mismatch between Gravatars doesn’t necessarily mean the emails are different
• Moderator-only information matches between the accounts (IP, email, or something else I don’t know about?)

Most of these answers are also upvoted by the community as a good match.

I already ask the user to merge their accounts when I have any reason to suspect they’ve created a second account but it’s rare that any of them stick around or respond. Beyond this, there’s not anything that even a moderator can or should do.

What reasons, if any, are strong enough for us to allow questions like this to be closed (or closed against) as a duplicate? The current policy (Closing Story-Ident questions as duplicates (where there's no acceptance)) doesn’t address this.

It’s pretty rare that this happens and a suitable duplicate also exists, but it does happen. For example, a question was recently asked and has an accepted answer but I’m not sure if this is a suitably accepted duplicate: Book series my dad told me about. It involves space travel, clones, and an indigenous people with kangaroo tails

Answer 1

Since I closed this question: Sci-fi novel series with older people transferring their minds into younger bodies as a duplicate of this one: Book series my dad told me about. It involves space travel, clones, and an indigenous people with kangaroo tails, I will go ahead and answer this question.

I did notice that in the older question, the question and answer were not posted from the same Stack Exchange account. However, I adjudged that we could reasonably presume that the two accounts were created by the same person. If the answer was posted by a trouble-making troll, that would be one of the most profoundly subtle trolls I have ever encountered.

The most obvious thing is that the two accounts do use the same handle, "Chris L." Note also that neither Chris L account has been used to post anything else on SF&F—just the question for one account and the answer for the second. The question answer were also posted just one day apart, just what you might expect from a new user who posted a question, found the answer quickly on their own, and came back to post the answer. They just happened to have lost their account credentials in the brief interim. Ideally, Chris L would merge their accounts; however, it is not uncommon for new users to appear, ask a single question, and then pay no further attention to the site.

However, others may disagree. If people generally feel that the identity of the questioner and answerer is not sufficiently confirmed, then we can reopen the duplicate. If the question is reopened, that will have the advantage of providing a bright line rule for dealing with cases like this in the future. If the duplication closure stands, there will have to remain a certain element of best judgement in handling cases like this that arise in the future; however, these instances are sufficiently rare that they can, if needed, be discussed individually here on Meta.