Preheat the oven to 350 degrees F (175 degrees C). Heat dates, brown sugar, orange juice, and orange zest in a saucepan over low heat. Cook, stirring occasionally, until dates have softened, absorbed the liquid, and mixture is like a paste, about 10 minutes. Remove from heat and stir in vanilla. Stir oats, flour, brown sugar, baking soda, and salt together in a bowl. Cut in butter with a knife or pastry blender until mixture resembles coarse crumbs. Lightly press 2/3 of the crumb mixture into the bottom of a 9x9-inch pan. Spread date mixture evenly over the crumb crust. Sprinkle remaining crumbs evenly over the top of the date mixture. Bake in the preheated oven until top is golden, about 30 minutes. Cool on a wire rack for at least 1 hour before slicing into bars. Yields 16 servings.