Regarding this question, I believe duping it to a question that was closed as off-topic is a bit disingenuous. I believe there was general consensus the question itself was on-topic. Is this really okay? Wouldn't it have been better to let the on-topic question stand on its own?
A kind golden hammer wielding participant has reopened my question.
Could we have/develop a rule or procedure for this?
The whole point of closing questions, I thought, was to make it easier to find authoritative answers to clear questions, so we wouldn't be reinventing the wheel all over the place, with some wheels coming out better/more useful than others, and the whole site looking like spaghetti code.
I don't see how closing a question with a closed question helps with that.
(However: if there's something inherently bad about the way the new question is posed, then by all means guide the OP (in this case me) toward improving the question, including closing it if necessary.)
Duplicates should point to a question that has at least one good answer that answers the question being closed as a dupe. In my opinion, the quality of the answers of the proposed duplicate are a bigger problem than the question being closed. The scoring of the handful of answers for the proposed dupe target seemed pretty low for EL&U, which means to me that the community wasn't that involved and the answers are suspect. If the questions are truly duplicates, the one with more community participation should be the "master" question in my opinion.
It's a simple thing for a mod to reopen a question that was closed for other reasons and re-close it as a duplicate to allow the higher quality question to thrive and attract answers that are better vetted by the community. A question that was closed for lack of research can be closed as a duplicate of a question that does have proper research without somehow tainting the well-asked question with "off-topicness".
The only hard and fast personal rule I have for choosing duplicates is that I never choose a question that has no significantly up-voted answers unless the questions are exact duplicates.
Bear in mind that the "off-topic" close reasons include our three custom reasons, and that "off-topic" simply means "does not conform to one or more expectations".
Certainly, one of those expectations is that the question should be of a type allowed in the list in the Help pages. But other expectations are explicitly stated in the close reasons, and these appear in the banner on closed posts. You need to read the banner text.
"Questions on choosing an ideal word or phrase must include information on how it will be used in order to be answered. For help writing a good word or phrase request, see: About single word requests"
In this case, the question may well have conformed to the list in the Help, but it didn't meet the standards required for its tags.
Nevertheless, it has answers. Those answers may well suffice for other questions, such as the one you reference here. If they do not, then questions which are closed as duplicates should be edited to say why the nominated duplicate doesn't provide an answer.
It is perfectly reasonable for questions which are on-topic but lacking in detail to be nominated as duplicates, if the answers are reasonable.
There may be more of a grey area where a nominated duplicate has no answers and has been closed already. However, it's also entirely possible that closing as a duplicate of such a question is exactly the right thing to do (eg in the case where both questions are of an equal standard). In such a case, the closure serves as a pointer to question quality: "Look, here's a question just like yours which was closed."
I believe a general bar on nominating closed questions as duplicates is unsustainable. That must be permitted. (And if it were A Bad Thing, then the system would not allow it at all.)
In the case in point here, there's probably enough in the question not to close it for want of a sample sentence; and it's probably sufficiently different from the "duplicate" that reopening is reasonable.