If it did not get "attention" (which I interpret as 10+ karma, but that's my interpretation), it may be resubmitted.

If the last "attention" is older than a year, resubmitting is also okay.

The first part is in the FAQ, the second part has been said by the mods multiple times.

I searched and found several instances of a similar link, but HN doesn't stop me from posting it. I'm guessing there's some decay algorithm or it's not checking sub-domains or deep-links.