I should have thought of this when I posted the question, but it was late... The StackOverflow answer is here:

How StackOverflow handles duplicate questions

Here's a summary of that answer:

• Don't tag duplicate questions with "duplicate"

• A question should only be closed if it's an exact duplicate of another question.

• If you have enough rep to edit the question, add the following at the top of the question:
  ^{_{This now gets automatically added when closing as a duplicate}}

   ###Duplicate
   > [title of question](url to question)
  

• If the question is similar to another one, add the following at the bottom of the question:

   ###See also
   > [title of question](url to question)
  

• If you can't edit the question, leave a comment with a link to the other question.

I should have thought of this when I posted the question, but it was late... The StackOverflow answer is here:

How StackOverflow handles duplicate questions

Here's a summary of that answer:

• Don't tag duplicate questions with "duplicate"

• A question should only be closed if it's an exact duplicate of another question.

• If you have enough rep to edit the question, add the following at the top of the question:
  ^{_{This now gets automatically added when closing as a duplicate}}

   ###Duplicate
   > [title of question](url to question)
  

• If the question is similar to another one, add the following at the bottom of the question:

   ###See also
   > [title of question](url to question)
  

• If you can't edit the question, leave a comment with a link to the other question.