The “view on dash” xkit extension is kind of broken sometimes which means it doesn’t show your post but it WILL show what your dash would’ve looked like at the time that you made it.
This includes posts made by people you’re following now that you weren’t following then.
Long story short, you can use that extension, if you wish, to give a time capsule of what your dash would’ve looked like at any point in your blog’s history WITH the people you’re following now included.
Rush's tumblr archive 