If they don't get picked up at the initial newborn screening, it's more common for kids not to get picked up until they are 3 or so. Looking at it that way, thank goodness he's getting checked into at 20 months! It's fantastic that you do have some early intervention help coming in, they're so good about finding games and type of play that focus on what your child needs, while keeping it all fun.
As for not picking up on anything, kids are way too smart for their own good sometimes. They learn every way of compensating, without even thinking about it. For kids with a hearing loss, they learn to look around a lot, so they don't miss anything. They get really tuned in to the little vibrations when someone opens a door or walks across a room, so they learn to turn and look. They pick up some basic lip reading of the words that are used all the time.
Even with my son, who without hearing aids can only barely hear you at all, I forget and don't notice from time to time. It's be early in the morning, or right after nap and he won't have his "ears" in yet and I'll go on talking and chatting to him, forgetting that he can't hear me. And he responds! Sometimes he'll say "what?" a little more often, but not always. He looks up when I call his name, he laughs when I call him silly names, he comes running when I offer a cookie. This from a boy who really, honestly, can't hear me. I forget and don't notice his hearing loss, and I know for sure it is there.
For the happy, positive stories side of things...
DS has had hearing aids since he was 5 weeks old. Even with them, he had NO babble until he was 16 months old. None. He said "ah" and that was it until 16 months. Now, at 2.8 or so, he never stops talking. Never, not even in his sleep! Anyone can understand what he says, as well as you can any child of his same age. His vocabulary is off the charts ("mama, I'm making a barricade so the dinosaurs can't get in my room," "Mama, I no have apples in my restaurant, you want pizza instead?") There is nothing in the world that is slowing this boy down.
). After he had fallen asleep they attached the electrodes to his head and did the test. So it is possible to do it without sedation!
