I found that only certain posts show up when you get into the discussion through Dear Prudence. Now, if you click back into the Fray by clicking up on the left onto the "Dear Prudence" link you see, it will bring you to ALL the Fray posts about Prudence.

It's a quirky little thing I noticed when the revamped the Fray. And annoying. So, it depends on "where you were" when you posted. If you were already in the full Fray lists, it won't show up if you go through the original Dear Prudence Discussion link later on.