The backdate entry feature seems to come up a lot in support and it isn't very well documented. For example, if you backdate an entry and then want to edit it, you can't just edit last entry or last 20, you have to go to the day of that entry or use the pencil icon. And editing entries has the same weakness as the memory feature for people who don't allow comments. Editing that might be a good idea, but I doubt it matters for most people unless they backdate their entries. So I wrote up everything relevant I could relating to the backdate feature so someone could rework it if they wanted to. Although I have no idea how the clients handle it since I don't use them. Anyway, if it's helpful, here it is.
The backdate entry feature is designed to let users add entries to their journal that belong significantly earlier than their current entries. Such as adding entries from a previous journal. Without the backdate feature their friends would suddenly be swamped with a large number of very old entries. The backdate feature prevents the entry from showing in the normal journal view and on friends pages. The entry will only be visible from the calendar.
You should use the feature only if you don't want the entry to appear in your normal journal view or to show up on your friends pages.
If you wish to edit a backdated entry you can do so in one of three ways. You can go to your calendar, click on the link for the day of the entry, and then click on the comments link. Above the entry will be a pencil icon that allows you to edit the entry. The second method is similar. You go to the calendar view and select the subjects link for the month the entry is in. Then select the entry itself from the subject listing and use the pencil icon to edit the entry. The third method is to go to the edit page at http://www.livejournal.com/editjournal.bml and
select the edit day option. Fill in the date for the journal entry and a list of all your entries for that day, backdated or not, will appear. Select the correct entry and you can edit it.
If you backdated an entry and have now changed your mind, you can unmark backdating and the entry will appear normally again.