Those tests say that but in actual fact in most cases it's not true. They make that claim based on women who implant early in their TWW and so 5 days before AF is due is actually a few days after implantation. Most women don't implant that early and it can just give you a confusing reading.
If you can get your hands on a FRER (First Response) they're generally the most accurate.
In terms of symptoms, unfortunately they don't mean a lot. Your hormones are all over the place in the TWW even if you've been unsuccessful. I know some cycles I've had symptoms in the TWW and been convinced (mostly I don't get any TWW symptoms) but it's turned out to be a BFN. When you're looking for symptoms and expecting to see them, it's amazing what your body can tell you. But in saying that, you could be pregnant. My MC cycle I had days in my TWW where I felt fine and others I felt terrible. The day I started bleeding I lost all my symptoms.