We actually went through in-vitro just last week. I don’t recall what the national averages are, but in our case, after taking the stimulation injections, they were able to retrieve 14 eggs. After doing intra-cytoplasmic sperm injection, 9 fertilized. After three days, 8 of them had undergone cell division with various rates of success. The embryologist recommended transferring 5 back in, which we had done (we will probably be lucky if one implants). The remaining 3 were frozen (at our ongoing expense) for possible use later.
Going through the stimulation is a big deal. For a while I was giving my wife 4 injections per day. I wouldn’t think that there are many couples who “forget all about their other fertilized eggs”.