True about the small margin between stall and overspeed, I didn't mean you could regularly fly like that. But according to the article, their air speed decreased from > 220knots to 90knots. What I meant was that regardless of wind, 90knots air speed should give you a ground speed so low that it should leave no doubt that you are stalled.

Apparently the PF was even thinking they were in overspeed at that point. So a ground speed should have told them that they weren't. But on the other hand, positive pitch angle and -10,000 ft/min vertical speed should also tell you beyond a doubt that you are stalled, so the problem here was not that the pilots didn't have the information they needed to figure out what was going on. They did, but failed to process it. It seems this is a classical case of "getting behind the airplane", they were just not processing events at the speed they were happening.