If you're seeing small air cells, and internal pips (i.e., noses sticking into the air cell), then you almost certainly had a humidity issue. BUT it has nothing to do with the humidity DURING lockdown. In fact, I generally recommend getting that humidity (during lockdown) as high as you possibly can--which is different for everyone.
It's the humidity the rest of the time that affects the air cell. What happens is that over the 15 days or so of incubation, the moisture inside the egg gradually evaporates, creating a larger and larger air cell. When the baby is ready to hatch, it pokes its bill/beak through the inner membrane into that air cell, and those are its first breaths of air. Like a human infant, once it starts breathing air into its lungs, it loses its ability to gain oxygen through the umbilical cord. Once it takes that first breath, it must continue to breathe.
With its beak in the air cell, the baby then rests for several hours--up to 48 hours in the case of a duck baby, only one to three hours in some cases with quail. It gather energy, strengthens its lungs, and uses up the air in that cell. When the oxygen starts to run out, it pips a hole in the outer shell to let fresh air in, then rests again (sometimes only for a few moments--again, in the case of ducks, this rest can last for up to 48 hours).
Unfortunately, if the air cell is too small, two things happen. One, it runs out of oxygen before it has gained the strength to punch a hole in the outer shell. Two, it can't rest properly because it has to raise its beak so high to reach the air--it's like standing on tippy toes, it uses extra energy.
Okay, so how does that incubation humidity affect this? The obvious answer is that lower humidity inside the incubator means more evaporation from the eggs, and that is partially true. Lower humidity=larger air cell. Of course, you have to be careful not to let TOO much evaporate, because the baby needs room in the moist part of the egg to grow, so you need a high enough humidity not to stunt the baby's growth.
Less obviously, the environment OUTSIDE the incubator affects this process as well. Think about it this way. When the air enters the incubator, it carries some moisture with it. If it carries a great deal of moisture, it can lose a great deal of moisture INSIDE the incubator without taking any moisture from the eggs themselves. If it comes in as dry air, however, then in order to reach a certain humidity level INSIDE the incubator, it has to take some moisture from the eggs. Thus, dryer air coming into the incubator means faster air cell development than when moister air comes into the incubator, even if the inside humidity is the same.
So the point is, whatever the books say to put your humidity at, start there, but it's not the end-all be-all. For best results, monitor the air cells for your specific circumstances, keep records, and then adjust until you find the optimal level for your situation.
Hope that helps!
Of course, having said all of that, the fact of the matter is that your hatch rate was TERRIFIC, and nothing to sneeze at.

These are just tips for getting even better results, since that's what you asked for.
Congrats on your sweet babies!!