Wow, I was really stumped with this one!  I couldn’t explain this answer very well in class but thought I could try and give you a better example here.  “Such and such” is used when we don’t know, it’s not important, doesn’t matter, in a secretive way when we don’t want some people who are present to know what we are talking about, or when there are multiple possibilities and we want to indicate that all of them.  Similarly the phrase so-and-so is used when talking about people.

When so-and-so gets here, act naturally

(don’t want other people present to know who you are talking about)

They agreed to meet at such and such an hour.

(it really doesn’t matter what hour they met, and the speaker possibly doesn’t know)

We often hear that such and such a piece of information cannot be released into the public.

(refering to any possible pieces of information that this aplies to)

Hope this helps!!

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