Okay, I don't know whether to start a new thread or just continue here, but I have a more clear description of what is happening, because I have a more clear understanding of it now after trying some things. I'll write it here because technically this remains unresolved.
I created a test user to see if I would be able to see the comments on the "private" posts like apparently most of my readers can. I was able to view them, and the comments, and the individual archive page. So I upgraded that user to administrator status with a user level of 10 to see if somehow it was either of those things that made me get the error (and maybe only me, since when I am logged in as someone else everything works just fine).
I could still see the posts as long as I was logged in as someone else. I discovered that if I deleted a user, I could attribute all posts and links to another ID, so I created another user with an identical name to my admin and deleted the admin, then attributing all of the admin's posts to my new user (because remember, the new user could see the comments and the individual archived posts and also, in the preview window when creating a post could see the post). As soon as I attributed all of my posts to the new user, the new user suddenly is getting the very same "sorry, no posts matched your criteria" error.
This is only happening on private posts, which until this all began to happen, were visible to users at level 2 and above. Still are, apparently, except the admin. Or rather, except for the author of all of the blog posts.
I have a test user if someone wanted to login. The username is 'testy' and the password is 'login'
You'll see that you can see private posts and view comments.
So I guess the question is, is there something somewhere in the code, or the database, that is somehow creating some block for the author of the posts only? Where might I look for such an attribute, and how would I change it? Am I way off base with my thinking?
Also, am I being clear? I am trying to explain this to the best of my ability but I know that sometimes I forget simple details that need to be there. My own little oversight.
Oh, and also, was it really really stupid to delete my admin account? And if it was, is there any way to get it back? My new user account has exactly the same permissions as the admin did, but I'm wondering if there is something else about the admin account that I might not be aware of that is necessary to the functioning of the blog.