By the time of Oscar Hammerstein II’s death, in August of 1960, The Twilight Zone had completed its first season on CBS, and The Lawrence Welk Show was six seasons into its 16-year run on ABC. It’s worth noting this not because one of the theater’s greatest librettists was a known fan of either TV show, but because both programs may come jarringly to mind at Doreen Taylor’s Sincerely, Oscar, a combination memoir and homage that celebrates the talent, and apparent immortality, of the man whose timeless work ranges from “Oh, What a Beautiful Mornin’” to “Some Enchanted Evening.”