Yep, give it a shot. If they never hatched before, at least this would be something different to try :) rule out things one at a time and you will get some!
50-60% is "usually" way too high for most folks around here. How humid is it where you live? Local conditions make a big difference. If you live somewhere arid and dry, you can run a little higher, but if you live somewhere humid (like me), I run with absolutely no water in my incubator until...
It was still alive?? Wow!! There were in an incubator and no way it was added later than the rest? Sounds like it would have to be a cool spot, or maybe a very old egg? I think older eggs tend to take longer to develop. But a week slow sounds a bit excessive.