newspaper dates at the library

I am thinking I must just be confused because this makes no sense to me at all and seems too obvious to be an oversight. When the girls go to the library to look for old newspaper articles about Dear Johnny's death how how could Roberta find an article on her mother? They were supposedly there to look for articles from 1945 (and at one point they even mentioned something like 'well it didn't happen in April' as if they are clearly looking month by month of that particular year). Taking place in 1970, if Roberta was 12 then her mother couldn't have died any earlier than 1958 or 59. If anyone has an explanation for this, please clue me in - it just seems way too obvious to be an oversight on the part of the writers. They make a point of riding their bikes all the way to that other town so they can look at the old archived newspapers that go further back than the library in their own town. Thanks for any input!