It doesn't show you all of them (at least from what I've found). Sure, you find most of them but I stumbled upon a very high LL lost sector that certainly was not on the map and I nearly didn't make it all the way through. I think it shows all boxes, and highlight lost sectors that are within your LL range. Once your at max LL you might be able to see them all. But I could be wrong. I just swear I didn't see a Lost Sector on the map and got my face stomped in repeatedly.