Chicks dying during incubation because of excess humidity is NOT the same thing as chicks drowning. It's a very badly misused term. An embryo can fail to develop and die at any stage of the incubation. And excess humidity can be the cause of the embryo dying. But a chick can only drown AFTER it has pipped internally into the air cell and started trying to breathe air. If there is excess fluid in the egg at this time, the chick can inhale it and drown. But before it pips into the air sac, it isn't breathing air, so how could it drown?
So a chick that has drowned will have pipped internally into the air cell. It might also have pipped the shell. If you're doing carton hatching I think it would be quite easy to see. Break a small hole through the shell into the air cell and have a look. If it has broken through to the air cell then drowning is a possibility. Tip the egg up and see if any fluid drips out. At this stage of development and hatching, there should be almost no liquid left in the egg so if fluid drips out, the chick most likely did drown. I think a chick that drowned could have either an unabsorbed yolk sac or an almost totally absorbed one, depending on whether it drowned immediately after breaking through to the air sac, or after 12 hours of resting and absorbing the yolk. That is definitely possible, depending on the positioning of the egg. Also even with lots of fluid in the egg, the chick might be lucky and not drown. If it manages to keep its beak above the fluid, it can still hatch okay.
A chick that hasn't pipped internally into the air cell has NOT drowned. It may have died during incubation due to excess humidity conditions, but technically, it has not drowned. So do the same thing and have a look in the egg. If the chick looks almost fully developed but it hasn't broken through to the air sac, break the egg open into a bowl and see if it looks like there is a lot of excess fluid. The more fully developed the chick is, the less fluid there should be.
Like Cowboy says, there are loads of other reasons for late deaths apart from excess humidity or drowning...