Turning the eggs is like a lot of the other guidelines or recommendations on this forum. Following the guidelines doesn't guarantee success and failing to follow them does not guarantee failure. All they do is improve your odds of success. I don't always follow all of them to the letter and there are some guidelines I don't even know about, and I do OK.
Compare most of the guidelines to when you are driving. Something can go wrong when you drive. You might have an accidient. Even if you violate the guidelines of safe driving, you are not guaranteed an accident every time. Sometimes you can run red lights or stop signs and not have an accident. Even if you follow all the guidelines of safe driving that you know, you can still have an accident. A deer can run in front of you or a tire can blow out. Or someone else can run a red light. No guarantees either way. But if you follow the guidelines of safe driving, you are less likely to have an accident. If you follow the hatching guidelines as best you can, you improve your odds of a good hatch.
Are some of the guidelines over the top? Yes, I think they some are, just like some of the speed limits in certain places are over the top. Some people evidently think that rules against texting while driving are over the top since they continue to do it, but those of us that have had friends or relatives killed or seriously injured because someone was texting while driving do not consider them over the top. I guess it's a matter of perspective.
A couple of bad things can happen if you don't turn them. When body parts are developing, which is mostly very early in incubation, they can form in the wrong place if the egg is not turned. Things like the internal organs are out of place or maybe both eyes are on the same side of the head. Most of these don't survive until hatch. This does not happen all the time and it is not guaranteed to happen, just that it might.
If the egg is not turned, the yolk or developing chick can contact the inside of the egg shell. The egg shell is porous. If the yolk or developing chick touches it, it can dry out and stick to the egg shell. If they continue to develop, which most don't, they can't position themselves for hatch or move to zip. Again, this does not happen all the time, but it can happen.
How serious is not turning them during the second week of development? I don't know. Most body parts are formed the first week, so you should be OK from that aspect. The one I'd be more worried about is the developing chick sticking to the inside of the egg shell. I honestly don't know what the odds of that happening at that stage are. I'd certainly carry on with incubation and I'd still expect most of the chicks to hatch. You've hurt your odds of success but you have not guaranteed failure at all.