That's the way the duplicate detection works here on HN. A recent exact match becomes an upvote, because if you think it's worth submitting then you would obvi

That's the way the duplicate detection works here on HN. A recent exact match becomes an upvote, because if you think it's worth submitting then you would obviously think it's worth upvoting the original. On the other hand, since old discussions are closed, repeats are allowed after a certain time. Likewise, if the URL isn't an exact match, it's not recognised.