Watching director Theodore Melfi’s “Hidden Figures,” about the African-American women working for NASA who were instrumental if not indispensable to getting our first man in space, we scratch our heads and can’t help but ask ourselves, “How come I didn’t know this?” But figuring the truth here isn’t rocket science. So many years after the fact, it’s the same depth of prejudice that hampered Katherine G. Johnson, Dorothy Vaughan, Mary Jackson and their sister colleagues from convincing the space agency of their genius that has squirreled away their story.