There's no title-matching algorithm. The duplicate detector only considers URLs.
Beyond that, I'm not sure I get your point. It's definitely intended that reposts be allowed if (and only if) a story hasn't had attention in about a year. You have to change the URL slightly to make the repost work, and that's by design. Merging threads doesn't solve the problem we're talking about here, where the previous post didn't get much attention, since you'd be merging into a dead thread. The problem merging solves is the opposite one, when you have multiple active threads on the same story, and we do merge threads when we see that.
Better dupe detection is on our list to work on, but it's a harder problem than it sounds and I don't know when we'll get to it.
Beyond that, I'm not sure I get your point. It's definitely intended that reposts be allowed if (and only if) a story hasn't had attention in about a year. You have to change the URL slightly to make the repost work, and that's by design. Merging threads doesn't solve the problem we're talking about here, where the previous post didn't get much attention, since you'd be merging into a dead thread. The problem merging solves is the opposite one, when you have multiple active threads on the same story, and we do merge threads when we see that.
Better dupe detection is on our list to work on, but it's a harder problem than it sounds and I don't know when we'll get to it.