Hitting a wall

Both of my parents were adopted. My mother searched for her birth parents until she passed away in 2004. She also searched to find my fathers birth parents also. I have been very curious to learn about my family tree and being able to trace that back but since my mother passed away from lung cancer, it is very important to me to also find out about the health history of my biological grandparents family also. I have spent a few years searching using the non identifying information that my mother had gotten for both her and my father. These papers have given me what would seem like very good places to start but I haven't been able to really find any promising leads. Some examples would be that my mothers birth fathers parents died in a car accident when he was 5 which would mean that it happened around 1937. It turns out car accidents were quite common at that time and it is hard to find articles that include names. From my fathers non identifying info I used the dates of his birth mothers siblings to search yearbooks since there was a set of twins which I thought would narrow it down, I then matched these names with names of possible siblings in the grades they would have been in at the time. I was left with a very large list since it seems many people had very common last names at that time. There was updated information given about 25 years ago that may hold some clues to but again, I have found no pieces that seem to fit this puzzle right. I did notice an interesting thing about the writing on the non id papers themselves that I have been trying to figure out if it's realistic to try the idea. I noticed that there is a line where the blanked out information is but underneath that line there are the bottoms of letters in some spots, it seems that I could maybe figure out possible words by using the bits I can see and the length of the space. Has anyone ever considered this or maybe tried to attempt this? Any ideas on other search techniques or any advice will be greatly appreciated. I am determined that I will find a way to find them, it's becoming unlikely that my parents birth parents would be alive at this point and I haven't decided if it's right for me to contact their families if I should find their names and I don't think I will be sure what to do when I find the information but I have no plans to give up.