It depends how fast people are answering other posts - they just move down the way if other threads are answered after yours. It's only ever the six latest posts which show.
There are only six answers showing in 'Latest Posts' so I presume that if more than six people post an answer at around the same time, some of the answers won't show.
Ah - yes, there is a time limit on it, too. With the Apotheosis thread, we have to remind the Ed that it needs to show up in LP, at the beginning of each new month.