Please define criteria for "new content"

Hi there. I have read the related help files but need one thing clarified. I have a newsletter that goes out on the 1st of the month at 3 a.m., when there’s new content.

Can someone please clarify for me what the criteria for “new content” is? Does this mean a blog post that was posted the same day the newsletter will be going out? OR, does it mean any post that has been published since the previous newsletter went out?

Thanks in advance. I’m trying to figure out when to schedule my blog posts to ensure the newsletter WILL go out.

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