Well, I did semd a PM to steet, and this was the reply I got:

This depends on the definition you give to "creation" : if your fanfic has been created in september, then it's the date that is shown here. Although yes, the "send date" should probably be the date when you stated it was ready.

I used to only keep one date for fanfics : the creation date and that's all. Now I record all the important dates such as the moderators validation date : that will be the one used for displaying the "last fanfics sent". It's not yet - I have to work on that.

I think it's not a big deal though, as long as your fanfic is online. Just promote it by other ways, such as posting it in your signature, or talking about it on the forums/shout boxes etc...

Sounds like right now, there isn't much that can be done to fix it.

How do I do that?

If it's a bug, send steet a detailed report on it and he'll surely fix it when he has the time. If you don't report it nothing is going to be done.

Well, I sent a PM to Lone Wolf_fanwriter about the matter, and the response I got was that it was most likely a bug, as no one controls what the sent-in date says.

This is most likely a bug...But, if it's the fanfic mods who set the date for sent fanfics, then maybe it was human error.

Though, somehow, I doubt that it's set manually...

Anyway, your best bet would be to PM a fanfic mod, which are listed in the "Site" section (The tab with Steele's head on it) under the subsection "Staff".