From the guidelines:

> Are reposts ok?

> If a story has had significant attention in the last year or so, we kill reposts as duplicates. If not, a small number of reposts is ok.

In other threads, the mods explained that the dupe detector is weaker than expected on purpose so good stories get a second (and third, ...) chance to get popular. Sometimes the first submission don't get attention by bad luck (wrong time, another submission was too popular, random, ...). So it's common to see that the second or third resubmission gets to the front page.